The European Union wants a transition period after Brexit to end no later than Dec. 31, 2020, according to the European Commission's negotiating directives agreed yesterday.

The development comes after EU leaders last week signed off on the first stage of Brexit negotiations, ending more than a year of stalemate over Britain's bill for leaving the bloc, as well the fate of the Irish border and EU expatriates.

"The transitional arrangements should apply as from the date of entry into force of the Withdrawal Agreement and should not last beyond 31 December 2020," the published text showed, as reported by Reuters.

Coinciding with the end of the EU's current seven-year budget period, the end of 2020, 21 months after Brexit at the end of March 2019, had long been expected as the target end date of the transition but this was the first official confirmation that this is the official goal of the Union negotiators.

British Prime Minister Theresa May had formally asked for a transition to last around two years.

The four pages of new directives for EU chief negotiator Michel Barnier were in line with guidelines issued by EU leaders at a summit on Friday and will form the basis of talks on the transition which Barnier hopes to start next month.

They spell out that Britain will be effectively still a member of EU institutions, bound by all their rules including new ones, while not having a say in their making. The EU will also offer Britain a non-voting place at some meetings where decisions may affect specific issues and will set up special arrangements for a UK role in setting annual EU fishing quotas.

The directives also spell out more clearly that EU treaties with other countries and international organizations will no longer apply to Britain during the transition period. However, the document adds: "Where it is in the interest of the Union, the Union may consider whether and how arrangements can be agreed that would maintain the effects of the agreements as regards the United Kingdom during the transition period."

As she presses for the quick transition deal, Prime Minister Theresa May faces opposition from hardline eurosceptics in her Conservative Party over the EU's terms.

May has already accepted in theory the continued jurisdiction of the ECJ and that London will have no legal basis to conclude its own trade deals during the period.

Influential pro-Brexit lawmaker Jacob Rees-Mogg slammed this demand as "rather hostile", leaving the UK "no more than a vassal state, a colony, a serf of the European Union," according to AFP.

May insisted to British lawmakers on Monday that the transition is necessary as it would provide continuity for businesses and individuals until the future relationship could be resolved.

She repeated that Britain would be leaving the EU's single market and customs union, but said the transition arrangements were "a practical matter that most people will understand and appreciate".

The next phase comes as Barnier ruffled feathers in London on Tuesday with a warning that any ties after Brexit would inevitably result in Britain's financial companies losing full rights to trade across the bloc.

This was a consequence of "the red lines that the British have chosen themselves. In leaving the single market, they lose the financial services passport," Barnier told a group of European newspapers.