Some EU officials have also held up a potential delay in issuing the guidelines as a means of pressuring Britain to more quickly finalize talks on a withdrawal treaty and a transition period that is to follow Britain's exit. "And what we're doing today is highlighting that fact", opposition Labour lawmaker Chuka Umunna told Reuters.
The plans say there are "only a small number of areas" where the two sides disagree.
"The EU wants a transition of 21 months, we want a period of around 24 months", the source said, adding that Prime Minister Theresa May previously left out the implementation phase extending beyond the around two-year period.
The EU wants May to clarify how she sees Britain's future relationship with the bloc.
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.
But the prime minister's spokesperson played down the significance of the language on the length of the transition period. That meeting should also allow the start of negotiations on the future relationship.
According to the document, first published by Bloomberg, London says that although the transition is likely to last for two years, the duration should be determined by how long it takes to "prepare and implement the new processes and systems that will underpin the future partnership".
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Having a transition period, or implementation phase, that is based on the principles of the World Trade Organization, implying that the transition should be accepted only if a free-trade agreement with the European Union is guaranteed.
Britain is due to leave the European Union in just over a year.
Theresa May will attempt on Thursday to bridge the rifts within her Cabinet over Brexit and unite senior ministers behind an agreed approach to negotiations with Brussels. They will try to come up with a final version of her government's approach to possibly the most hard phase of the negotiations - settling on a transition phase and final agreement.
Morgan is pairing up with the Labour chair of the home affairs select committee, Yvette Cooper, for an event in parliament with the CBI on Wednesday where they will warn of the risks for Britain if it fails to secure a strong customs arrangement after Brexit.
The letter published on Wednesday called on Mrs May to ensure that Britain had "full regulatory autonomy" from the European Union as well as being free to negotiate and sign deals with other countries.
The letter included a series of suggestions for Theresa May, such as asking for "full regulatory autonomy"; only complying with the EU's vision for a transition period "if the final deal is fully negotiated"; and make sure the United Kingdom can negotiate trade deals with "third countries" as soon as it leaves the EU.