The Independent understands that any push-back operations would have to meet numerous conditions, including the presence of French authorities to receive vessels.
But Paris has suggested it will not cooperate with the plans, with a letter to Ms Patel from her French counterpart earlier this year saying the “use of maritime refoulements to French territorial waters would risk having a negative impact on our cooperation”.
It comes after the number of asylum seekers crossing the English Channel hit a new daily record of 1,185 on Thursday, following rocketing attempts since the home secretary vowed to make the route “unviable” in August 2020.
Official legal advice that was leaked this week suggested that government lawyers believe that any push-backs will be met by legal challenges, and the Home Office is likely to lose.
When questioned about the legality of the planned operations last month, Ms Patel said a “framework” had been drawn up but admitted: “There is a narrow basis for the operationalisation of this tactic.”
Labour accused the home secretary of “blaming everyone but herself” for unprecedented numbers of people risking their lives to cross the English Channel.
Nick Thomas-Symonds, the shadow home secretary, said: “Labour has called out the push-back technique as unconscionable and wrong-headed. It is unsurprising that government lawyers believe the technique would not be considered legal if brought to a court challenge, and yet the home secretary persists with it.
“This is a clear sign of desperation from the home secretary because of her failure to grip this crisis. She must take responsibility, show leadership and change course.”
The Independent understands that rules drawn up for Border Force mean that targeted boats have to be in a designated portion of the English Channel, and to have reached that area independently without being led or coerced.
The vessels must be assessed by drone to look for numerous signs of “vulnerability” that The Independent has decided not to publish.
If a dinghy enters the push-back area meeting all of those criteria, the Border Force will still have to back off if the situation deteriorates.
Crucially, French authorities have to be present during a push-back operation and be willing to receive the boat.
A House of Commons library briefing published in September said the United Nations Convention on the Law of the Sea allows countries to prevent passage to prohibit smuggling, or breaching immigration rules, “but any return of a vessel to a state’s territorial waters would require that state’s consent”.
A letter from French interior minister, Gerald Darmanin, in September said its position on rescue operations in the Channel remained unchanged and “safeguarding human lives at sea takes priority over considerations of nationality, status and migratory policy”.
He added: “The use of maritime refoulements to French territorial waters would risk having a negative impact on our cooperation.”
An official from the ISU union, which represents Border Force staff, said the “very strong view of staff is that push-backs are never going to happen”.
“The constraints on when this would occur at all are so tight that we simply do not believe there will be a situation where this will ever happen,” Lucy Moreton told The Independent.
“Even if we could identify a suitable vessel we would still need the French there, in a situation where the French say they won’t do it because they don’t think it’s legal.”
Ms Moreton raised concerns over safety, echoing fears that passengers could attempt to damage boats or threaten to jump overboard when stopped.
“As the pressure is placed on people they’re not going to turn round and say, ‘Gosh, it’s got a bit difficult, I think I’ll go home now.’ Things will just get more extreme,” she said.
The home secretary has said she wants to force the boats back to “save lives”, and that people will not be endangered.
But Ms Moreton said Border Force staff were “spooked” by a clause in the new Nationality and Borders Bill creating partial immunity against prosecution in the event of deaths at sea.
The draft law states: “A relevant officer is not liable in any criminal or civil proceedings for anything done in the purported performance of [push-back operations] if the court is satisfied that the act was done in good faith, and there were reasonable grounds for doing it.”
Other parts of the controversial bill formalise Border Force powers to stop, board, divert and detain vessels in the Channel if an immigration offence is committed, and to use force.
The proposed law also makes it an immigration offence to cross the Channel without permission.
In October, a UN refugee agency (UNHCR) official said push-backs would “unavoidably” put lives at risk and may not work as a deterrent.
The UNHCR’s UK representative Rossella Pagliuchi-Lor added: “There is an obligation to both save lives at sea and not endanger lives at sea, which would almost unavoidably happen if there were attempts at turning back dinghies which are overcrowded with people.”
The Home Office declined to comment on its rules for push-backs or any legal advice received.
Dan O’Mahoney, the Clandestine Channel Threat Commander, said: “Migrants making these dangerous crossings are putting their lives at risk and it is vital we do everything we can to prevent them and break the business model of the criminal gangs exploiting people.
“As part of our response it is important we have a maritime deterrent in the channel and Border Force officers are authorised, trained and stand ready to use safe and legal options to stop these deadly crossings.”
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies