Turning back migrant boats heading across the Channel to the UK would be a “highly dangerous” tactic if adopted, an ex-Border Force chief has warned.

Tony Smith, former Border Force director general, said the UK’s top priority should be “the preservation of life above all else” and called for a diplomatic solution to its war of words with France over efforts to tackle migrants crossing the Channel by boat.

His comments come following reports that Home Secretary Priti Patel had sanctioned tactics to turn back migrant boats towards the continent to stop them from making the journey to the UK.

Speaking to the PA news agency, Mr Smith said such an approach would be “highly dangerous”, adding: “These vessels are already unseaworthy to start with.”

“These are very small boats that are overloaded, we’ve already had drownings,” he said.

Mr Smith continued: “We’re getting vulnerable people, women and children, not just young men, in them, overloaded in… vessels and the top priority in my book, under the UN Convention of the Law of the Sea, is the preservation of life above all else, and so both the French and the British should be committed to that, and making sure that nobody dies.

“If you’re going to introduce a tactic like this, particularly unilaterally, without the agreement of the French, then what you’re saying is you spot an unsafe, overloaded vessel in the ocean, but you’re going to turn it around and push it back or try and keep it out of your territorial waters.

“How long are they likely to survive in that circumstance? What happens if the boat capsizes or somebody drowns?”

He said Border Force did have the capability to board vessels, but said any such approach would be “putting our own officers at greater risk as well as the migrants in any confrontation at sea”.

“I don’t think blockading the English channel is realistic frankly, and I’m really worried that we’re going to see more lives lost,” he said.

“And I’m really worried about who would be held responsible in those circumstances, because I certainly wouldn’t want it to be the UK Border Force.”

Mr Smith, who retired in 2013 and is now a global border security consultant, said that in Australia, human smugglers were known to “drill holes” in boats when its border force was spotted so they had “no choice but to pick up the people”.

He said that during his time at Border Force it was deemed “very unlikely” that the UK would see “large-scale migration by maritime methods”, with efforts concentrated on preventing entries via lorries and implementing checks at Calais in northern France.

He said: “I think it came as a bit of a surprise when they did start arriving.”

Mr Smith explained that existing legislation was “not really geared up towards what we would call interdiction on the high seas” – where a vessel would be intercepted, stopped and if necessary redirected or seized.

“Those things haven’t been something that traditionally we’ve done in this country, not for migration, we have for drugs and for commodities where there’s been criminality, but not migrant smuggling before now,” he said.

Mr Smith argued that the problem the UK faced was a lack of agreement with authorities in France on how to handle migrant crossings, claiming they were “not cooperating with us”.

He said there should be a “diplomatic agreement” between the UK and France where there are joint patrols by the nations on the Channel and once rescued migrants are “safe and well” they are “taken instantly back where you came from”.