The former head of the Borders Unit at the Organisation for Security and Co-operation in Europe (OSCE), the world’s largest intergovernmental security organisation, says “successive governments have dismantled the layered mosaic of border security” which once protected Britain’s coast.

Henry Bolton, who served as an army intelligence officer and police detective before becoming arguably the foremost border security expert in the United Kingdom, spoke exclusively to Breitbart London after terror watchdog David Anderson warned that the country’s “smaller south and east coast ports, marinas and landing places” are vulnerable to “returning foreign fighters or other terrorists” from extremist organisations such as Islamic State.

“David Anderson is absolutely right when he says that our maritime borders are porous”, Bolton agreed, citing factors such as the erosion of the Coastguard, which once passed information to the authorities through a network of hundreds of permanently-manned and auxiliary stations, but now operates from a small and ever-shrinking handful of Maritime Rescue Co-ordination Centres.

Bolton also raised concerns about the diminishing “legal responsibilities of harbour masters to monitor, record and report vessel movements” at the many ports, piers, and jetties which ring the British coastline.

Last April, the Leave.EU campaign smuggled a group of “migrants” across the Channel from Gravelines in France to Folkestone Harbour in just two and a half hours, “totally unopposed” and in “broad daylight”, to highlight the seriousness of the situation.

“This is Folkestone Harbour,” announced the pilot as he disembarked. “No harbour master, no police, no customs, no nothing.”

Bolton attributed the blame to Britain having “no comprehensive multi-agency border strategy” and the “swingeing cuts” which have “crippled the capability and morale of the UK Border Force”.

Last June, shortly after a rare catch of a pair of Iranian migrants who crossed the Channel successfully, it was revealed that the Border Force had just three cutters available to patrol almost 8,000 miles of coastline. Italy, by contrast, has around 600 craft monitoring a coastline which is less than 5,000 miles long.

Alarm bells have previously been raised by Admiral Lord West, former head of the Royal Navy, and David Bolt, Chief Inspector of Borders, among others.

While the threat from drug-smugglers, gun-runners, and people-traffickers is particularly acute, Bolton was at pains to point out the more general implications with respect to large-scale illegal immigration, exacerbated by European Union (EU) regulations. The bloc’s rules make it very difficult to deport migrants who arrive after mounting illegal sea crossings, forcing their way on to lorries or even storming the Channel Tunnel.

Bolton singles out the Dublin III regulations in particular. These prevent the UK from simply deporting migrants who arrive via safe countries, unless it can be determined which EU country they first arrived in and what their country of origin is. Many migrants refuse to divulge the relevant information and destroy their passports. Consequently, only 49 out of several thousand illegal arrivals could be sent back to France in 2014.

The issue raises questions about the priorities of the Conservative government, which is led by politicians who campaigned to Remain in the EU. The party cut £36 billion from UK public spending in 2010-15 alone, assisted by the Liberal Democrats – but £85 billion (gross) or £42 billion (net) in membership contributions was handed to the EU over the same period.