Robert Mugabe has long claimed that Britain wanted to overthrow him, using this to smear his political opponents as Western stooges and shore up support for his kleptocratic regime in Zimbabwe. He has warned over the years of looming invasion, of hit squads sent to kill key aides and gunboats despatched from London.

These claims have been dismissed mostly as the paranoid ravings of a deluded despot. But now they have been given force by Thabo Mbeki, the former South African President, who claims that Tony Blair suggested their two nations invade Zimbabwe to topple Mugabe.

It is hard to imagine British armed forces fighting their way into Harare to oust a man who, for all his many faults, was an elected leader and liberation hero to his people. But given subsequent events, it is worth asking – if only in the interests of counter-factual history – whether it would really have been such a bad idea.

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This may sound an absurd question. But consider the facts. Mbeki said the former British Prime Minister urged him to join a “regime-change scheme” involving military force shortly after the turn of the century, a period when Zimbabwe was slumping into one of the most catastrophic collapses in modern times.

Mugabe had already been in power for two decades by this time, inheriting the richest nation in Africa and wrecking it with his corrupt cronies. Britain, like other Western powers, had ignored the slaughter of 20,000 rival supporters in Matabeleland and indulged him as an ally in the Cold War while he tightened the noose on his nation.

But by the start of this millennium Zimbabwe was in a mess and Mugabe’s misrule could no longer be overlooked. The economy was in freefall, aided by a disastrous intervention in the Congo war, while rivals were eliminated, journalists silenced and dissidents tortured. Meanwhile, the HIV/Aids pandemic had started to rip through the population just as state services were crumbling and donor support was drying up.

To distract attention, the campaign of white farm seizures was unleashed, a brutal and short-sighted solution to necessary land reform. It was around this time that Blair – once dismissed as “a boy in short trousers” by Mugabe, who loathed New Labour – was allegedly discussing intervention.

Nothing happened, of course. But over the next few years Zimbabwe endured the world’s fastest-shrinking economy as the second-worst hyperinflation in history –peaking eventually at 231 million per cent, with prices doubling almost every day – ravaged the country. People would go to the bank to get blocks of money that was so worthless it would not cover the bus trip home. Prices in stores soared even as shoppers queued to check out.

Families spent weekends traipsing across borders to buy basic provisions in neighbouring countries; the Beit Bridge over the Limpopo heaved with heavily laden buses, cars and pedestrians taking food back to a fertile nation once known as “the breadbasket of Africa”. As the government handed once-thriving farms to supporters, shops were shutting and millions of Zimbabweans were starving. Hospitals were chained closed and medicines unavailable, leaving women to die in childbirth for lack of the most simple treatment.

Life expectancy crashed to the world’s lowest – just 34 years for women and 37 for men at one stage. Little wonder that an estimated three million people – one-quarter of the population – fled the country, while unemployment rose to about 90 per cent for those that remained.

Mugabe prided himself on Zimbabwe having the highest literacy rates in sub-Saharan Africa. But many of those fleeing were the educated elites frustrated by his regime, and he was content to see potential opponents leave. This was the backdrop to the 2008 election when a weary country voted for Morgan Tsvangirai, only for Mugabe’s allies to refuse to quit, unleashing horrific political violence in response. Eventually, the warring parties were forced into uneasy coalition by diplomats led by Mbeki, who secretly threatened senior figures with the International Criminal Court.

The introduction of the US dollar stabilised the economy and life expectancy has risen – although it remains eight years lower than when Mugabe took power and repression remains routine. Most Zimbabweans are still unemployed, poverty is endemic and public services struggle. Even in the prosperous suburbs people rarely have running water. I joked with one man about the green water in his pool when I was there in July; he replied that it was his main supply for bathing and laundry. He washes from a bucket each day.

Meanwhile, a gangster government in cahoots with China preaches communism while creaming off vast sums from the nation’s mineral wealth, especially the world’s biggest diamond mines in Marange. An official source told me that in one year these should have delivered more than £1bn to the state, but only £23m was handed over.

After another dubious election victory this year, delivered on the back of anti-British rhetoric, the 89-year-old dictator is pressing ahead with fresh indigenisation policies. Rather than wreck the economy again, however, he is focusing on bakers and beauticians rather than bankers and mine operators – let alone the white business people who aid his regime.

These claims of Blair’s desire for intervention will fuel the ruling party’s paranoia, especially at a time of palpable tensions between two camps fighting to succeed “the old man”. Blair rapidly denied Mbeki’s allegation – perhaps mindful of how his prime ministership was so disfigured by the foolish invasion of another foreign country a decade ago. But it is worth remembering not all his overseas interventions were so disastrous. In May 2000, as the Zimbabwean meltdown intensified, he sent a small force of British troops to Sierra Leone to shore up successfully a government threatened by vicious militias.

It is ludicrous, of course, to contemplate Britain leading an invasion of Zimbabwe just 20 years after it won independence. As Mbeki said, it is not our responsibility to decide who leads the people of an African nation. Equally, it is impossible to determine whether the whisky-drinking President’s recollection is accurate given the emphatic denial by Blair – not that the former Labour leader has always proved the most reliable witness in history.

Yet, at the same time, it is impossible not to wonder what would have happened if the South Africans had agreed to lead a military assault to remove the revolting regime that corrodes their neighbouring nation. They called him “the crazy old man”, after all, according to one leaked diplomatic cable. For if they had sent in troops to that shattered state 13 years ago, would Zimbabwe have endured a far less traumatic time and been in a much better place today?