PRIME Minister Theresa May has been accused of siding with "cynical Brexiteers" with her refusal to pursue a customs union with the European Union.

SNP Westminster leader Ian Blackford told Mrs May she and her Government were "not working in the interest" of the British people with her approach to Brexit.

Mrs May, responding to the accusation at Prime Minister's Questions, told MPs that the British people "voted to leave the single market and customs union" - to heckles and cries of "that wasn't on the ballot paper" from the Labour and SNP benches.

Mr Blackford said: "The CBI, the NFU, the Scottish Government, the Welsh Government, the House of Lords and overwhelmingly members of this House want the UK to remain in the customs union.

"Why is the Prime Minister on the side of her cynical Brexiteers? Frontbenchers are not working in the interest of all nations of the United Kingdom."

Mrs May responded: "The British people voted to leave the European Union, in voting to leave the European Union they voted to leave the single market and the customs union.

"What we want to ensure is that we as a country are able to independently negotiate free trade deals around the rest of the world, that we are also able to ensure that we deliver on our commitment for no hard border between Northern Ireland and Ireland and that we have as frictionless a border as possible between the United Kingdom and the European Union.

"What businesses tell me is that they want that tariff-free, frictionless border and that's what we're negotiating for them."

Mr Blackford responded telling Mrs May her answer "wasn't good enough", adding that the Government was "bereft of ideas" on the Northern Ireland border issue.

Mrs May hit back telling MPs the SNP Westminister leader was "wrong in so many of his statements".