The british government has launched a secret consultation with the maritime industry to explore constructing floating walls in the channel to block asylum seekers from crossing the narrow strait from france, according to a leaked document.

The home office has approached maritime uk, a trade group, seeking help to stop migrant boats from crossing into uk waters. one of the requests included the option of temporary marine fencing in one of the busiest shipping lanes in the world.

The latest proposal is one of a series of controversial projects home secretary priti patel has asked officials to explore in a bid to stop clandestine asylum seekers entering the uk. crossings by migrants using small boats in the channel has risen almost fivefold this year compared with 2019.

The financial times revealed this week that another option considered by ms patel was to use ascension island over 4,000 miles away as an asylum processing centre.

The times reported on thursday that migrants could alternatively be processed on disused ferries or even decommissioned oil platforms in the north sea.

The ft also revealed this week that some officials had floated the blue-sky idea of barriers or booms in the channel to stop boats reaching shore or even using pumps to create waves to push boats back towards france.

An email from maritime uk on september 17, obtained by the ft, shows that the idea of floating barriers is now being seriously pursued by officials. it revealed that the home office was launching a consultation with industry to identify potential solutions to the small boats challenge.

It said the joint security and resilience centre, which is part of the home office, was working with the border force and dan omahoney, a former royal marine who was recently appointed as the clandestine channel threat commander by ms patel.

Those bodies were seeking a discreet reaching-out to shipping organisations to explore options such as marine fencing and other water-based technologies to block boats, the document said.

Industry members were invited to put forward ideas or proposals by september 21. maritime uk emphasised that the consultation was highly sensitive and urged discretion from members.

One industry figure said the proposal was unethical and perhaps not legal.

The email said the home office wanted the capability to fully prevent a slow-moving, heavily overloaded migrant boat from making progress.

The solution would have to be deployable to a precise location and capable of remaining there without accidentally entering french waters. it would need to be rapidly deployable and rapidly removable given it would be used in busy shipping lanes.

The memo added that the solution had to be safe for those who come into contact with it and for those operating it.

Maritime uk said on thursday that it did not believe the plan was legally possible. the group said that as the umbrella organisation it was often a conduit between industry and government.

The home office engaged us to pass on a question around options to inhibit passage to uk territorial waters, which we gave to our members, it said. the clear view, which we shared with the home office, was that as a matter of international convention, that this is not legally possible.

The home offices top civil servant refused to be drawn on the various proposals on thursday when he appeared before a session of the house of commons public accounts committee on asylum accommodation.

Matthew rycroft, permanent secretary, said: what i can confirm is that the civil service has been responding to ministers questions about how other countries deal with what is a global issue migration.

We will be leaving no stone unturned. no decisions have been taken. no final proposals have been put to ministers or anybody else. this is in the realms of the brainstorming stage of a future proposal.

Mr rycroft insisted the department would take into account the uks international legal obligations in framing proposals for ministers.