The U.K. government should be prepared to request an extension of the March 29, 2019 Brexit deadline, and should also consider prolonging any transition period, according to a report by an influential group of British MPs.

Aspects of the report are certain to infuriate the most ardent supporters of Brexit. And its findings underscore the continuing deep divisions within the British government over the best ways to manage the country's departure from the EU.

The report is the third by the Commons Brexit select committee, which compromises 21 MPs. And the committee itself is apparently sharply divided over the findings, with a narrow majority voting to approve the document.

Among the most controversial points is the suggestion that the U.K. might request an extension of the two-year deadline for exiting the EU, which could only be granted by unanimous agreement of the remaining 27 EU countries.

"If more time were needed to negotiate the Future EU-UK Partnership, the Government could seek an extension to the Article 50 period," the committee writes in the report, which is to be published Sunday.

"This would require unanimous agreement amongst the EU27. It would allow more time to negotiate a detailed Political Declaration and potentially more time to negotiate the treaties/agreements that will establish the Future Partnership before the start of the transition/implementation period, depending on the length of the extension."

The committee also notes it could make sense to extend the transition period, which the EU envisions lasting until December 31, 2020. Prime Minister Theresa May has referred to those roughly 21 months following withdrawal as an "implementation period" — but there is no indication that a sweeping trade agreement and other aspects of the future relationship between Britain and the EU will be ready for implementation at that time.

"If a 21-month transition/implementation period is insufficient time to conclude and ratify the treaties/agreements that will establish the Future Partnership or to implement the necessary technical and administrative measures along with any necessary infrastructure at the UK border, the only prudent action would be for the Government to seek a limited prolongation to avoid unnecessary disruption," the committee writes.

"It would, for example, be unacceptable for business to have to adapt their import and export processes twice. We therefore recommend that the Withdrawal Agreement include a provision to allow for the extension of the transition/implementation period, if necessary, and with the approval of Parliament."

The contents of the report, which are already proving highly divisive within the U.K., were first reported by the Huffington Post.

The U.K. and the EU are hoping to finalize the transition agreement this week, for approval by EU27 leaders at a summit in Brussels on Friday. So far, however, there has been reluctance to include any reference in the transition agreement to a possible extension, even though both sides know that ultimately it may be needed.

The committee report said it agrees with May's outright rejection of a proposal by the EU, put forward in its draft withdrawal treaty, that would keep Northern Ireland within the EU's customs union, and effectively impose a trade border in the middle of the Irish Sea, as a way of avoiding any restoration of a border between Ireland and Northern Ireland.

However, the committee also has some tough words for May's government, noting that she has not yet put forward any proposal of her own on how to solve the conundrum of the Northern Ireland border.

"If the Government is unhappy with sections of the draft withdrawal agreement then it should produce its own suggested legal text," the Committee writes.