Margaret Thatcher would have voted for Brexit if she was still alive in 2016, the Iron Lady’s son has admitted on what would have been his mother’s 100th birthday.

Sir Mark Thatcher claimed his late mother would have held grave concerns about the European Union as a political institution, having once helped create the bloc’s Single Market.

Despite posing in an EU flag dress in the 1975 referendum on membership of the European Economic Community, Sir Mark told The Sun: “My mother’s relationship with Europe generally can be summarised very simply, in my estimation.

“She was a great supporter of any role, or any organisation, in which trade was encouraged, cross-border trade was encouraged. Because the more trade you have, the more jobs will come, the whole economy expands, it expands and everyone gains from that.

“When that happens, the Government gets more money through taxation and then there’s more money to spend on hospitals, pensions, and the like.

“Whilst it was an economic community, she was wholly supportive of it. She became less enthusiastic when it became a political union.”

Outlining the two reasons behind the Iron Lady’s increased sense of Euroscepticism, Sir Mark added: “She didn’t like large, amorphous masses of government in the first place.

“And the other thing was, she was deeply conscious of the fact that our Parliament has an extraordinary history going back hundreds of years, and she firmly believed that our Parliament, in Westminster, should be the one that actually governs the nation and not Brussels.”

Sir Mark, who is now 72, pointed out that more than a 35 per cent of parliamentary business was spent passing European legislation into law in his mother’s final year in power.

“Would my mother have voted to leave the EU?” Sir Mark asked. “Yes, it is my estimation.”

When pushed on her potential concerns about the economic consequences, Sir Mark added: “The debate within her mind would be is the potential loss of economic benefits a price that she would afford to pay in respect of recovering our sovereignty over Parliament and our own political and economic affairs.”

Debates about whether Mrs Thatcher would have been in favour of remain or leave first sparked in 2016 when the Iron Lady’s long-time foreign policy aide Charles Powell suggested his old boss would have campaigned for Britain Stronger In.

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Lord Powell said at the time: “She would never have backed Brexit. She’s far too sensible for that.”

Mrs Thatcher campaigned for the UK to remain a member of the EEC in 1975, with two-thirds of Britons opting to keep Britain inside the economic bloc.

However, after entering No10 in 1979, Britain’s first female Prime Minister became increasingly hostile to Brussels.

She first expressed frustration with the EEC in 1984 in a stand-off about Britain’s financial contributions.

Mrs Thatcher secured an agreement whereby the UK, which has a relatively small agricultural sector, received a rebate.

However, the Iron Lady’s iconic Bruges speech ran a horse and coaches between her and her pro-EU Conservative colleagues.

“We have not successfully rolled back the frontiers of the state in Britain, only to see them re-imposed at a European level with a European super-state exercising a new dominance from Brussels,” the Iron Lady said in 1988.

Mrs Thatcher’s former Chancellor, Geoffrey Howe, went on to launch a scathing attack against the Iron Lady shortly before her resignation in November 1990.

He said: “The tragedy is—and it is for me personally, for my party, for our whole people and for my Right Honourable Friend herself, a very real tragedy—that the Prime Minister’s perceived attitude towards Europe is running increasingly serious risks for the future of our nation.”

Despite her role in creating the EU’s Single Market, Mrs Thatcher’s second Chancellor, Nigel Lawson, claimed in 2016 that Brexit presented the UK with an “historic opportunity” to finish the job his former boss started.

He said: “The next Government and the next Prime Minister will have a historic opportunity.

“The opportunity to make the United Kingdom the most dynamic and freest country in the whole of Europe, to finish, in a word, the job which Margaret Thatcher started, and to become a beacon to our European friends currently embroiled in a failed and doomed experiment.”

However, Mrs Thatcher’s ex-Deputy Prime Minister Lord Heseltine remains a steadfast Europhile, recently warning attendees at the Conservative Party Conference about the threat posed by Reform UK leader Nigel Farage.