Margaret Thatcher would have campaigned for Britain to quit the EU, a loyal friend revealed last night as he released an extraordinary letter written 23 years ago by the former Prime Minister.

In the never-before-seen correspondence, Lady Thatcher attacked the EU project as 'contrary to British interests and damaging to our Parliamentary democracy'.

Tory MP Sir Bill Cash, who was personally handed the note in 1993, said it was therefore 'simply inconceivable' she would have done anything other than campaign to leave in the upcoming referendum.

He said Lady Thatcher had given the letter to him with specific instructions to make it public if there was ever any doubt over whether or not she would have signed up to the 'European project'.

Sir Bill said now was that time.

Margaret Thatcher would have campaigned for Britain to quit the EU, a loyal friend revealed last night as he released an extraordinary letter (pictured) written 23 years ago by the former Prime Minister

Tory MP Sir Bill Cash, who she gave the note to, said it was 'inconceivable' that Margaret Thatcher (right) would have backed David Cameron's (left) renegotiation and voted to stay in

His move follows a hugely controversial claim by Charles Powell, who was Lady Thatcher's private secretary during much of her time in Downing Street, that she would have backed David Cameron's renegotiation and voted to stay in.

The revelation came on another day of drama and fevered speculation at Westminster and Brussels ahead of the expected June 23 referendum. Yesterday:

The president of the European Council said the continent's migrant crisis could lead to Britain voting to leave the EU.

Donald Tusk also warned that Europe was facing 'a dangerous moment' in its history similar to the 'day before World War One'.

The head of Nato said the migrant crisis was the 'most challenging threat' to the security of the military alliance in a generation.

A survey by ICM found the Leave and Remain campaigns are deadlocked at 50 per cent to 50 per cent among voters who have made up their minds – a two-point rise for Leave and a similar dip for Remain.

A senior eurocrat said the PM's emergency brake on benefits would do nothing to curb mass migration.

The head of the Conservative backbench 1922 committee predicted 100 MPs would vote against Mr Cameron's deal.

The lawyer wife of Boris Johnson attacked the renegotiation for not doing enough to curb the power of EU judges.

Lady Thatcher's letter to Sir Bill (pictured) was sent in the aftermath of the bitter parliamentary struggle over the Maastricht Treaty

Lady Thatcher's (left) private secretary during much of her time in Downing Street, that she would have backed David Cameron's (right) renegotiation and voted to stay in

Lady Thatcher's letter to Sir Bill was sent in the aftermath of the bitter parliamentary struggle over the Maastricht Treaty – which effectively gave birth to the modern EU, and put it on a course towards political and economic union. By 1993, Lady Thatcher had stepped down as PM and was no longer an MP, so did not vote.

Her note says: 'I understand it is being suggested in some quarters that I would have agreed to the Maastricht Treaty. May I make it clear that I would NOT (underlined) have done so.

Lady Thatcher's (right, with David Cameron) letter to Sir Bill was sent in the aftermath of the bitter parliamentary struggle over the Maastricht Treaty

'In my view it is contrary to British interests and damaging to our Parliamentary Democracy.'

Sir Bill, one of the PM's most trusted followers, said her comments on Maastricht should leave no doubt that she would wish to leave the EU the Treaty had gone on to create.

Releasing a copy of the letter to the Daily Mail, Sir Bill said: 'When she handed this note to me personally, she told me I was to produce it any time when there was a serious question about whether or not she would have signed up to the European project.

'It is inconceivable she would not have wanted to leave the EU. If you are going to veto Maastricht, you are saying you are not going to go ahead with the European project.

'She gave the letter to me for a specific purpose and she had trust in me that I would do what she wanted. I am now doing that. There has never been the same degree of necessity to (release it) as there is now.'

In an article in the Sunday Times, Lord Powell – who was Lady Thatcher's chief policy adviser in the mid-1980s – said she would have 'gone along with what is on offer' and backed Mr Cameron. He added: 'Margaret Thatcher's heart was never in our membership of the EU. But I am convinced her head would continue to favour staying in on the conditions now on offer.'

But Sir Bill, who enjoyed family holidays with Lady Thatcher, flatly dismissed this claim.

He said: 'I was very disturbed and deeply concerned that somebody who knew her so intimately should believe that she would have gone along with what is a completely undemocratic project. It is just inconceivable.'

Lord Tebbit, who served in Lady Thatcher's Cabinets from 1981 to 1987, said: 'Powell has forgotten what Thatcher did say about Europe in the House of Commons, memorably to the Delors plan – which is still the plan for Europe – and that was, 'No no no'.'

Lady Thatcher (right) attacked the EU project as 'contrary to British interests and damaging to our Parliamentary democracy'

The early-1990s battle over Maastricht – which almost toppled the John Major government – was one of the most bitter in the history of the modern Tory party.

The treaty, which led to the European Community being renamed the European Union, was a massive step towards political and economic union.