Media playback is unsupported on your device Media caption Jeremy Corbyn: "Which will last longer the Northern Rail franchise or her premiership?"

Jeremy Corbyn has compared Theresa May's handling of Brexit with the "shambles" in the UK railways as they clashed at Prime Minister's Questions.

The Labour leader said key documents, including the blueprint for future EU relations, had been "delayed" while customs proposals had been "cancelled".

But Mrs May said she was delivering on the 2016 referendum result while Mr Corbyn was trying to "frustrate" it.

It comes amid claims of cabinet tension over post-Brexit customs plans.

The BBC's political editor Laura Kuenssberg said there were concerns the latest plans on the customs backstop - what happens if there is no free trade deal or customs arrangements ready by the end of the transition period in December 2020 - would, in effect, mean the UK never leaving.

There were specific objections among Brexiteers, she said, that while the document says there should be a time limit on closer ties to the EU, it doesn't say either what that time limit should be, or whose decisions it will be to say when time is up.

Pressed on the issue at Prime Minister's Questions, Mrs May insisted that the UK would leave the EU, as planned, in March 2019 and the 21-month transition period - or what she has described as an implementation phase - would end in December 2020.

But Mr Corbyn said the PM's Tory colleagues were not "all as one" with her on that.

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Analysis

By BBC political editor Laura Kuenssberg

Sources who have seen the four page customs backstop document tell me that it is "anodyne", that it is like Hotel California, where the UK checks out and never leaves - essentially, it's not up to snuff.

The specific objections are that while the document says that there should be a time limit on closer ties to the EU, it doesn't say either what that time limit should be, or whose decisions it will be to say when time is up.

The document merely says that the backstop will "only be in place until the future customs arrangement can be introduced".

For Brexiteers, the lack of a firm deadline is hard to swallow. Secondly, there is what has been described as a fudge on the European court.

Read Laura's full blog

Mr Corbyn said the negotiations were in chaos, with no cabinet agreement on a customs framework and a promised document setting out the UK's negotiating position on trade and other issues "no where to be seen" ahead of a crucial EU summit later this month.

"When it comes to Brexit, this government has delivered more delays and more cancellations than Northern Rail," he said.

"The government's white paper is delayed, its customs proposals have been cancelled and it has ripped up its own timetable just like our shambolic privatised railways."

But Mrs May said Labour was standing in the way of progress on withdrawal despite voting to trigger exit talks. "Since then, they have tried to frustrate Brexit at every stage," she said.

She called on the Labour leader to rule out another Brexit referendum and said next week's votes on the EU Withdrawal Bill - on which the government faces potential defeat on a customs union and the question of a decisive parliamentary vote on the final deal - would "test the sincerity" of MPs to leaving the EU.

Mrs May also came under pressure from Tory MPs, with Crawley MP Henry Smith saying his constituents wanted her to get on with both Brexit and sorting out the rail mess.