The two countries have tabled a blueprint to overhaul European Union membership into four tiers, with the most closely aligned states forming an “inner circle”.
Other tiers would include current and future EU member states, as well as associate membership and membership of the wider European Political Community (EPC) which would be open to the UK.
Lord Heseltine told The Independent that the UK must urgently explore the idea as the “overarching majority of people in Britain see Brexit as a mistake”.
However, asked about the potential to join a new outer tier of the EU, Tory former business secretary and arch-Brexiteer Sir Jacob Rees-Mogg said: “I like the outer tier that we are currently in.”
Associate membership would form the bloc’s first “outer tier” and could include members of Europe’s single market who are not in the EU, such as Switzerland or “even the UK”, a paper put forward by France and Germany stated.
Associate members would not be bound to “ever closer union” and further integration, it said. They would also not participate in deeper integration in policy areas such as justice, home affairs and citizenship.
But they would have to commit to the “common principles and values” of the EU, the plans state.
Associate members would also pay into the EU’s budget, but with lower costs.
A second tier for outer members would not include any integration with EU law but would upgrade the underpinning of the European Political Community (EPC), of which Britain is a part. It would see free trade agreements in certain areas such as energy or defence, and would focus on cooperation on important issues such as climate and security.
The Labour leader said the meeting began with an “exchange of gifts” and covered topics including “the relationship between our two countries” and future “prosperity and security”.
Sir Keir stressed plans to “build” on the relationship between France and Britain if Labour wins power.
A European diplomatic source told The Times the plan was designed with Labour in mind, despite Sir Keir having ruled out rejoining the EU’s single market.
“It is carefully balanced politically to be a potential place for Britain without the need to ever rejoin the EU or to hold a referendum,” the source said.
Associate membership would not include a customs union, allowing Britain to keep an independent trade policy.
Lord Heseltine told The Independent Britain “must urgently explore” France and Germany’s plan.
The Tory former deputy prime minister said: “The remorseless pressure of public opinion is changing the dynamic of politics.
“The dam is breaking and there is increasingly a move towards integrating with Europe. This is an opportunity offered by France and Germany which should be seized upon.
“The overarching majority of people in Britain see Brexit as a mistake, even those who still believe in it agree it has never been possible to implement it.
“The Tories have at least recognised change is needed, firstly with Northern Ireland and the Windsor Agreement and then with Horizon, allowing cooperation on sciences and technology.
“While the Red Wall may be insurmountable on this side of the General Election, the pressure of events will push people of both main parties to dare to change and to make permanent links with Europe.
“This new plan between France and Germany must be explored urgently.”
And Gina Miller, the anti-Brexit campaigner, told The Independent the UK should “see this move as an opportunity to start” the process to rejoin the EU.
“This ‘onion’ option, forming part of an outer layer of the EU, is an olive branch from our European neighbours, but we must negotiate cautiously to make sure that we regain at least some of the influence we lost under Brexiteer extremism,” she said.