Former Conservative Prime Minister Sir John Major has warned Theresa May that she risks encouraging support for another independence referendum by pursuing a 'hard Brexit'.

Sir John is the second ex-premier to make a similar argument in as many weeks.

Less than a fortnight ago Tony Blair warned that since the Brexit result the case for independence had become 'more credible'.

A BMG poll for the Herald earlier this month also suggest that support for independence has increased since Mrs May made her 'hard Brexit' speech in January.

Mrs May prefers the term 'clean Brexit' to describes circumstances in which control over the UK's borders is prioritised over access to the single market during exit talks with Brussels.

In a speech at Chatham House in London, Sir John also said it would be reckless to "ignore the risk" posed by another independence vote and said that both Scotland and the rest of the UK would be diminished by a 'divorce'.

He said: "In Scotland, I believe a hard Brexit will encourage a second referendum on independence. This may seem improbable at the moment, but it would be reckless to ignore the risk.

"As we saw last June, emotion and national pride can overcome economic self-interest. If Scotland were to become independent, both Scotland and the whole of UK would be diminished. That cannot be ignored as Brexit evolves."

He also called for a special deal for Northern Ireland.

In his first comments since the result, Sir John, who campaigned for a Remain vote, also warned that the “divorce settlement” could cost more than the notorious £350 million a week to spend on the the NHS the Leave campaign claimed could come back from Brussels.

He urged the Prime Minister to be honest about the "hurdles" and potential outcomes ahead warning that ordinary people had been led to expect a future outside the EU that was "unreal and over-optimistic".

He also called on Mrs May to inject "a little more charm and a lot less cheap rhetoric" into the Brexit negotiations with other EU countries.

And he hit out at Brexiteers who tried to silence Remain voters as he warned that MPs could not be used merely as a "rubber stamp" on any deal.

Green MSP Ross Greer said: "If John Major thinks an independence referendum is improbable he's paying no attention at all. That being a commonly held view amongst UK Conservatives would explain the contempt they have treated Scotland with after the Brexit vote however. To them it seems we are an annoyance verging on an irrelevance. If that's the case, they are in for a surprise.

"Independence is the only way to avoid the damage of a Hard Brexit, estimated to include a £2,000 drop in the average Scottish income and to avoid the angry, isolationist Britain the Tories have us heading towards. We can go down with their ship or we can put our own future in our own hands and enjoy the prosperity which will come with it."

Labour MP Chuka Umunna said a 'hard Brexit' would cost jobs and damages our economy.

A No10 source said: "The Government is determined to make a success of our departure from the European Union – and to move beyond the language of leave and remain to unite our country.

"The decision to remain in the UK was made by the Scottish people in 2014 and all the evidence shows people in Scotland don't want another referendum."

In his speech, Mr Blair had warned: "There is the possibility of the break-up of the UK, narrowly avoided by the result of the Scottish referendum, but now back on the table, but this time with a context much more credible for the independence case.”

An SNP spokesperson said: “Scotland was told in 2014 that voting no to independence would mean staying in the EU – we were misled, and now the Tories think they can do whatever they want and get away with it. 

"A Tory hard Brexit would do huge damage to Scotland's economy with the potential to cost 80,000 jobs and hitting the living standards of families across the country.

"Scotland voted overwhelmingly to remain in the EU and the world's largest single market - and the Theresa May has no mandate to drag Scotland out against its will. 

"The Scottish Government has put forward compromise proposals that would keep Scotland in the single market and time is running out for the UK government to show it is taking those proposals seriously."