The House of Commons will be given an opportunity to vote on if there should be a second Brexit referendum, the Prime Minister has announced.

Laying out her plans to bring the Withdrawal Agreement she struck with the EU into law, Theresa May said the Bill would require MPs to choose if there should be a "People's Vote".

Speaking in London on Tuesday, she said there was "one last chance" for Parliament to approve her Brexit deal, which has been rejected by MPs three times.

The Withdrawal Agreement Bill will be brought before the Commons in the first week of June, with May touting a range of "new" changes to the deal, including on customs and the backstop.

It comes after cross-party talks between the Conservatives and Jeremy Corbyn's Labour to find a Brexit compromise collapsed last week.

On a second referendum, May said: "I recognise the genuine and sincere strength of feeling across the House on this important issue.

"The government will therefore include in the Withdrawal Agreement Bill at introduction a requirement to vote on whether to hold a second referendum.

"This must take place before the Withdrawal Agreement can be ratified."

The Prime Minister also announced the Bill will legally oblige ministers to try to conclude alternative arrangements for the Irish backstop by December 2020 to "avoid any need for the backstop coming into force".

She said: "Although it's not possible for (alternative arrangements) to replace the backstop in the Withdrawal Agreement, we can start the work now to ensure they are a viable alternative.

May contiued: "The new Brexit deal goes further.

"It will commit that should the backstop come into force the government will commit to ensure that Great Britain will stay aligned with Northern Ireland.

"We will prohibit the proposal that a future government could split Northern Ireland off from the UK's customs territory."

The PM also said MPs would be allowed to decide whether to opt for the government's proposals on a temporary customs arrangement with Brussels or Labour's plan for a permanent customs union.

May said a failure to reach agreement on Brexit would lead to a "nightmare future of permanently polarised politics".

SNP Westminster leader Ian Blackford said the Prime Minister should have made her speech before Parliament, describing her not doing so as a "breach of responsibility".