LONDON, Feb. 21 (Xinhua) -- British Prime Minister Theresa May's government was put on a potential collision course with pro-Brexiteers Wednesday after details were published of a deal Britain is seeking with Europe for a transitional period after it leaves the European Union.

May is committed to Britain leaving the EU next March, but what has still to be worked out is the length of a transitional period when details of a permanent trade deal will be thrashed out.

The proposals put to EU member states say the transitional, or implementation period, should last as long as it takes to prepare and implement the new processes and new systems to enable Britain and the remaining 27 EU member states to work together. The EU has already told Britain it wants any transitional period to end by Dec. 31, 2020.

Downing Street insisted that the period should not last any longer than two years, taking Britain's final departure to no later than March 2021. May's spokesperson denied the government was seeking an open ended period.

The Independent newspaper said Wednesday the moves on the end date confirms its earlier reports that Britain was considering asking for a longer period because it was not sure that the duration proposed by Brussels would give it enough time to prepare.

Brexit Secretary David Davis said the implementation period, as he refers to it, is a "bridge to the future" and only amounts to a short period in the EU's orbit.

Earlier Wednesday a letter was delivered to May signed by 62 Conservative MPs saying Britain must not be stopped from negotiating trade deals with other countries once it leaves the EU next March.

The letter, from the European Research Group, made up of Conservative MPs led by Jacob Rees-Mogg, has insisted that Britain must retain full regulatory autonomy after it leaves the EU with the right to change British laws and rules once it leaves. The MPs also want any implementation period to be based on WTO principles.

Paul Blomfield, Labour's Shadow Brexit Minister, commenting on the letter from the 62 MPs said:"This letter exposes the deep divisions that run through the heart of this Conservative Government.

"It is clearer than ever that Theresa May cannot deliver the Brexit deal Britain needs. She is too weak to face down the fanatics in her own party and to deliver a final deal that protects jobs and the economy."

The pro-leave United Kingdom Independence Party (UKIP) accused May of a Brexit betrayal by asking for a longer transitional period.

UKIP's interim party leader, and Member of the European Parliament Gerard Batten, said: "This is Brexit betrayal at its contemptible worst. It's time for May to go and for a genuine Brexiteer to step up for role of Prime Minister."

Battern claimed May will delay and impede Brexit in the hope of later overturning the democratic wishes of the people, adding: "This is barefaced treachery and cannot be allowed to stand."

During any transitional period Britain will have no EU voting rights, but will have to observe all existing and new European rules.

Ahead of a planned speech about Brexit later this week, May has called her senior ministers to a meeting at her official country retreat, Chequers, to discuss the government's strategy.