The country's most respected civil servant, TK Whitaker, has admitted that an almost bankrupt Ireland was in danger of losing its independence in the late 1950s.

In a new documentary, he reveals that former Northern Ireland prime minister Terence O'Neill expressed his wish to have Donegal added to the six counties.

Whitaker, voted the greatest living Irish person in 2002, is seen as one of the most influential figures in 20th-century Ireland. In an interview with TG4, the architect of Ireland's modern economy says he warned the government in the late 1950s that the almost-bankrupt country would have to go back to Britain if urgent action was not taken to get out of debt.

He said: "The country was in danger of losing its independence. I felt an obligation to try and put things right.

"I was bold enough to write a note to the then [finance] minister [Seán Lemass] of the day saying if we continued the way we were it wouldn't be long before we'd have to ask England to take us back."

The 93-year-old says baffled IMF officials, who had arrived in the country to speak with Taoiseach Eamon de Valera in the late 1950s about the country's finances, were treated to a version of his famous 1943 speech about his ideal Ireland

"He gave them an account very much like that of the comely maidens and so on. When he came out, the American leader of the IMF delegation said: 'Your prime minister is a strange man'. I think de Valera understood at the end that the speech he gave was only a dream."

In the documentary, Whitaker, who was finance secretary during the 1950s and 1960s, also reveals that French president Charles De Gaulle didn't want Ireland to join the EEC because of the country's close ties with Britain.

The Down-born civil servant, who was a close adviser to both Seán Lemass and Jack Lynch during their time in government, says he was responsible for setting up the first state talks between the Republic and Northern Ireland after partition as he had developed a friendship with Terence O'Neill.

He says the issue of Donegal was humorously discussed between taoiseach Seán Lemass and O'Neill at their ground-breaking lunch meeting in 1967.

"Seán Lemass had a very good innings there. Terence O'Neill told him he really regretted that the six counties were only six counties and the county he liked best of all, Donegal, was outside their scope.

"'Oh' said Lemass, 'You can have Donegal if you take [Neil] Blaney with it'," Whitaker says.

He also reveals that a fired-up Ian Paisley and his supporters threw snowballs at the state car he was travelling in with the then taoiseach Jack Lynch for a similar meeting at Stormont in the late 1960s.

"They were standing in the snow armed with snowballs which they threw at our car. They were not very good shots.

"But when we were getting out at the prime minister's residence you could hear Ian Paisley bellowing 'No pope here, no pope here' and Jack Lynch turned to me and said in his nice soft Cork accent 'Which of us does he think is the Pope?'"

The man who brought Ireland out of its economic shell in the second half of the 20th century says his greatest ambition now is to live to be 100.

T K Whitaker – Seirbhíseach an Stáit will be shown on TG4 on Monday 27 December at 8.15pm