Image caption Palestine 1938: Tegart steps out of his car

When the British sought to quell unrest in Palestine in the 1930s, they turned to an uncompromising Irish policeman, who came up with a drastic and expensive solution - a network of fortresses that today stand as monuments to a lost empire.

They don't make policemen like Sir Charles Augustus Tegart any more.

That's partly because they don't need to - Sir Charles was a colonial officer whose job was to keep the Union Flag flying over Britain's far-flung imperial territories.

But it's also because he was a man of his time, impossible to imagine in a world where policing is about suspect profiling, and forensic evidence and human rights.

Tegart was a tough guy in a world going through tough times.

He survived six assassination attempts in India and in spite of the danger he continued to drive around in an open-top car with his Staffordshire Bull Terrier riding on the bonnet.

They were dangerous days - a businessman who happened to bear a close resemblance to Tegart was shot dead by separatist militants who mistook him for the detective they hated and feared.

He liked to keep a defused bomb on his desk as a paperweight - a reminder of the dangers he faced and the enemies he pursued.

Image caption In 1934 an attempt was made to assassinate the governor of Bengal

When he threw it across the office one day in a fit of annoyance, it exploded - it hadn't been properly defused after all.

Tegart, it is reported, found the incident amusing. It's the way of history that we can't be sure that whoever else was around when he threw it took the same view.

Tegart was born in Londonderry before Ireland was partitioned, and he devoted much of his life to ensuring that Britain's other imperial possessions didn't follow his home country (or at least the southern part of it) out of the Empire.

He made his reputation in India, the metaphorical jewel in the crown of Empire which was so important to Britain that it also provided the real jewel in the actual crown.

Britain's relationship with its Empire was complex; it wasn't simply a question of a wealthy country exploiting a poorer one - although that was certainly a part of it.

The lofty belief that any country would benefit from the introduction of British institutions played a role as did the Christian missionary impulse. But at the heart of it was trade. As early as 1870, India got 22% of British overseas investment, and, on the eve of the World War I, it was the largest single market for British exports.

The United Kingdom had a lot to protect on the subcontinent, and it relied on men like Sir Charles Tegart to get the job done.

Holding the fort Sir Charles Augustus Tegart (1881-1946) joined the Indian police in 1901, immediately after graduating from Trinity College Dublin

Became deputy commissioner of police in Calcutta, in charge of Special Branch, at a time of revolutionary turmoil

Later rose to become commissioner of the Indian Police and, in 1931, a member of the Secretary of State's Indian Council

Sent to Palestine by British authorities to advise on security during Arab Revolt (1936-1939)

Oversaw construction of reinforced concrete police stations and a frontier fence along Palestine's northern border

In 1942 appointed to head British wartime anti-black market operations

Like other colonising powers of the period, Britain tended to treat its subject peoples like children if they accepted imperial authority and like potential terrorists when they didn't. That was where Tegart came in.

His methods wouldn't stand up to much modern scrutiny. Long before the world hit upon the euphemism "enhanced interrogation techniques", he was reputed to take a violent and uncompromising way with detainees.

There were gun battles with Indian militants and there were the assassination attempts. But there was also the development of sophisticated techniques for collecting political information - the political context may have changed, but modern intelligence officers would still recognise some of the challenges he faced and some of the ways in which he faced them.

India was not the only trouble spot in the British Empire, of course.

In the 1936, the Arab population of Palestine revolted - partly in protest at the British decision to allow Jewish migration into the Holy Land from Europe.

To the British, all the problems were interlinked, because the Empire itself was interlinked.

Palestine was the "hinge of empire" - it guarded access to the Suez Canal, which in turn offered the shortest and cheapest route to bring troops and trade to and from India.

There was surely only one man to advise the British police force in Palestine on how to deal with political unrest. Sir Charles was duly sent for. His solution was drastic - and dramatic.

To prevent Arab gangs bringing arms and weapons south into Palestine from Lebanon and Syria, he proposed creating a line of fortresses.

Each would be strongly built to resist bombardment, siege and direct assault. There'd be plenty of storage space for ammunition and supplies. And there'd be a fence too - a long one. Around the new fortifications, British tactics would change. There'd be aggressive patrolling to deter incursions.

It's sometimes said that one of Sir Charles's predecessors at the top of Britain's Palestine Mandate Force believed that there was a key difference between policemen and soldiers. One worked with a notebook, the other with a rifle.

Sir Charles's police officers would be cut from rather different cloth.

Tegart was rather more than a courageous, effective opponent of the enemies of the British Empire.

In an age of austerity and strict control of public spending, he knew how to get things done in government too.

There is a narrative of British history from the late 1930s and early 1940s with which we are familiar - Chamberlain and Churchill, Munich and Dunkirk, the Battle of Britain and the fight for survival.

Tegart worked in parallel with that familiar story, and it's a reminder of how important Palestine was to the British that, in that direst hour of national emergency, several million pounds was spent building this extraordinary network of fortifications.

The historian Dr Gad Kroizer, of Bar-Ilan University in Israel, has published a book chronicling of the whole project and says simply: "The British saw Palestine as strategic, because it controlled the way to the Suez Canal and to India via Transjordan and Iraq. They spent £2,200,000 on these buildings... it's unbelievable how they used that money for the fortresses and not for their armies in Europe."

If you're a British taxpayer, look away now.

Sir Charles Tegart's methods of doing business wouldn't stand up to modern scrutiny any more than his alleged techniques for interviewing suspects. But he was a can-do guy.

Image caption Then... Image caption ... from the other angle... Image caption ... and at the planning stage in 1940 previous slide next slide

The memoirs of David Hacohen, a director of the Jewish building firm Solel Boneh, record how Tegart told him his company had got the job. There was to be no competitive tendering process.

When he warned Tegart that there weren't enough stockpiles of barbed wire under British control to complete the project, he records the Irish police officer's reaction:

"Tegart laughed and said he didn't own any shares in British companies that produced barbed wire. We were free to buy it wherever we wanted and wherever we could."

They ended up getting it from Mussolini's Italy.

The network of forts was built at startling speed.

Image caption Acre fort

The first buildings on high ground provided a screen across Palestine's northern frontier. In time, more fortresses were built at strategic points - near busy road junctions, river crossings and seaports. By the end of the building programme, there were 69 Tegarts - the smallest would house a company of soldiers (around 100 men in the British system). The larger examples would serve as substantial military headquarters.

They were all squat, forbidding structures in biscuit-coloured concrete, with plenty of narrow slits to provide firing points for defenders and bullet-proof steel shutters on every window.

For a soldier's eye view of the buildings, I turned to Campbell Aitkenhead, of the Parachute Regiment, who was based in a Tegart fort at Ashkelon on the Mediterranean after the end of World War II.

"In appearance," Campbell says, "they always reminded me of the fort you see in the Gary Cooper film Beau Geste. But from our point of view, they were very comfortable. We had been used to living under canvas, so with lights and shower facilities and an old Roman well as a source of water, we regarded them as good."

Image caption At least two Tegart forts are now museums - another is used to store garlic

So Tegart had got the buildings right. But the world changed around his well-designed and well-constructed fortresses - and the order they'd been built to protect was simply swept away.

Before WWII, the British facilitated the migration of Zionists into Palestine - the Jewish population increased from 175,000 to 384,000 between 1931 and 1936. As a result, the British found themselves fighting Arab militants in a revolt that started in 1936 and ended in 1939.

After WWII, Britain worked to prevent the arrival of Jewish refugees even though the Holocaust had created an unprecedented reservoir of Jewish despair in the blighted camps of Europe.

The British found themselves at odds with the United States which pressed for permissions to be granted for a further 100,000 Jewish migrants.

At one point, Britain intercepted a ship called Exodus 1947 filled with Holocaust survivors and sent it back to Germany, of all places, in what we would see in the modern world as a public relations disaster. Where once it had fought Arab armed groups Britain now found itself fighting Jewish militants.

Image caption Abed Saleh Abu Gosh served in the Palestinian regiment of the British Army

At any given moment in the 10 years between 1938 and 1948, British policy must have made sense to the men who made it - but it's hard to find any consistency in it now.

If you talk to the people who were there, those years immediately after the end of the WWII in Palestine feel tense, chaotic.

I met up with Abed Saleh Abu Gosh, who'd served in the Palestinian regiment of the British Army in the war and was offered a job by British intelligence as a bodyguard when it was over, as the crisis in Palestine deepened.

Abed Saleh is a good talker - and his stories have real chaotic, end-of-empire feel about them.

Image caption Abed Saleh later became a bodyguard to a British intelligence officer

"We travelled together in a car in plain clothes - we moved about pretty freely, with no fear," Saleh says. "He [the British intelligence officer] was disguised as a priest. He'd sit in front and drive - and I'd sit in the back in my civvies with a Tommy gun hidden under the carpet."

I wouldn't claim to be an expert in these matters, but I have seen an empire collapse in the old Soviet Union and I'd say the moment when your police officers are travelling about disguised as men of God with sub-machine guns hidden under the carpets in the car is the moment when the game is up.

In 1948, having alienated substantial portions of both communities, Britain left Palestine - effectively trying to hand responsibility over to the international community.

People were saying that no-one would ever conquer one of these buildings Eliezer Fuchs, Former Israeli Army fighter

When the UN decided that Palestine be partitioned into two states - one Arab and one Jewish - Israel declared independence, and the Arab states around it invaded with the intention of strangling the Jewish state at birth. It was just 10 years since the British had embarked on that costly network of strongpoints which had been seen as an investment in the imperial future.

Tegart's forts were front and centre in the war of 1948.

The British handed the keys of some of the buildings to forces who'd shown them loyalty - that included some Jewish organisations as well as some Arab police officers.

Some forts like the base at Latrun on the road between Jerusalem and Tel Aviv were the scene of heavy fighting. But this is not the story of that war - only the network of forts around which it raged.

No-one doubted their quality.

In a quiet street in the centre of Jerusalem, I met Eliezer Fuchs, whose story is perhaps typical of the stories of many of the young Jews who fought in 1948. He was born in Poland and came to Palestine in search of a place of safety.

Image caption 22 Jewish fighters were killed in one of the attacks to capture Nebi Yosha fort

He found himself in the thick of the fighting - a young sapper in an infantry unit that had made a series of unsuccessful attempts to capture one of the impregnable Tegarts which had been left under Arab control. The fort known as Nebi Yosha in Arabic stands on high ground overlooking the road from Rosh Pina to Metula, now on the border between Israel and Lebanon.

Image caption Eliezer Fuchs successfully campaigned to have Nebi Yosha called Fort 28

A series of attacks by the fledgling Israeli army had been repulsed - in one of the assaults alone, 22 fighters had been killed."

In the end, Eliezer led the attack in which the fortress finally fell - blowing the hinges off one of the reinforced steel doors with ball of plastic explosive which he'd chewed to make it malleable enough to mould around the lock.

He told me what the Tegarts looked like from the attackers' point of view.

"On this particular fort," he says, "there were two south-facing doors, both made of steel. All the windows - and they were narrow slit windows - had the same kind of protection. They had everything they needed inside to sustain themselves completely for months. People were saying that no-one would ever conquer one of these buildings - and in plenty of places where they tried all the attackers were killed."

The buildings live on - and there's no reason to suppose that they won't still be in service 100 years from now

In later life, Eliezer campaigned successfully to have the fort renamed Metzudat Koach - Fort 28 in Hebrew - to commemorate the total number of Jewish fighters who died in the battles to capture it.

In military terms, the forts were every bit as effective as Tegart must have hoped - even if they ended up in the hands of Arabs and Israelis rather than in the hands of the British who paid for them.

Most of them these days belong to Israel, although there are some on the Occupied Palestinian Territory of the West Bank. At least two Tegart forts are now museums and another is currently being used to store huge amounts of garlic on a kibbutz in the Jordan Valley.

But it is some kind of testament to the quality of their design and construction that plenty of the fortresses are still being used for their original purpose - if not by their original occupants.

Image caption The Israeli Border Patrol insignia bears an image of the Nebi Yosha fort

Their location once marked a line between British-controlled Palestine and Arab territories to the North which the British saw as a reservoir of support for Arab revolt in the land they were governing. These days they stand on the border between Israel and Lebanon and the troops and border police cleaning their rifles and eating their lunches in the cafeterias are Israeli.

Sir Charles Tegart was spared the experience of watching the sudden disintegration of the old world order he'd spent his entire life defending. He died in April 1946.

Just over a year later India became independent - a political development which would presumably have horrified him. Another year after that Britain gave up on the Palestine Mandate - the light was fading fast across the Empire on which the British used to say the sun would never set.

The buildings live on - and there's no reason to suppose that they won't still be in service 100 years from now.

You could regard them, I suppose, as monuments to an empire that was lost. I prefer to see them as monuments to the simple, eternal truth that no-one can ever know from one year to the next how history will turn out.

Image caption Matat fort - one of the first built - still in use on the border with Lebanon

You can hear Kevin Connolly's radio report on Charles Tegart on the BBC Radio 4 Broadcasting House programme website.