FILE PHOTO: The British flag flies next to European flags at the European Commission in Brussels, Belgium December 8, 2017. REUTERS/Yves Herman

BRUSSELS (Reuters) - European Union and British negotiators aim to agree before Nov. 25 on the maximum length allowed for extending the post-Brexit transition period under Britain’s withdrawal deal, an EU official said on Thursday.

This detail has been missing in the draft withdrawal agreement approved on Wednesday by Prime Minister Theresa May’s cabinet. The deal faces an uncertain future as several of her ministers resigned on Thursday and some lawmakers in the UK parliament have vowed to vote it down.

Under the draft text, there can be only one such extension of the status-quo transition. EU leaders are meeting on Nov.25 to rubber-stamp the draft agreement.

The EU official also said any extension of the transition period would have to be decided along with the appropriate level of UK contributions to the EU’s joint budget that would correspond to the scale of London’s continued involvement in the bloc’s affairs.