The DUP is still staying tight-lipped on whether it was financially backed by Fred Fraser — one of the developers who bankrolled the café business of Iris Robinson's teenage lover.

Both the party and the family of the late tycoon have also made no comment on whether he helped buy a bulletproof car for Peter Robinson in the 1980s.

An authorised biography of Mrs Robinson published in 2006 referred to an armour-plated vehicle being purchased for her husband after police had withdrawn security.

The book said businessmen had “clubbed together” to buy the DUP politician an armour-plated vehicle.

“Purchased at auction, the car had once belonged to the Shah of Iran,” it said. “With bulletproof glass as well as armour-plating to body and chassis, not to mention a gas extraction system, it was undoubtedly a well-secured vehicle.

“Both Iris and Peter were overwhelmed by the generosity.”

The biography — Iris: An Intimate Portrait — did not name the businessmen involved in the gift.

It said Mr Robinson's police security was withdrawn after his arrest during the loyalist invasion of Clontribret in the Republic in 1986.

Replying to Belfast Telegraph inquiries yesterday, a PR company acting for the Fraser family said it would not be making any comment.

The DUP has meanwhile stonewalled repeated questions.

Mr Fraser died in 2008 shortly after giving £25,000 to help the new riverside café business of 19-year-old Kirk McCambley.

The money was solicited by Mrs Robinson who was having a relationship with the youth at the time.

A further £25,000 was provided to the business by another developer, Ken Campbell.

Mr Campbell confirmed earlier this month that he was a past donor to the DUP, having made a one-off contribution of £4,000 to £5,000 a number of years ago.

DUP Environment Minister Edwin Poots this week revealed that Mrs Robinson had made representations over the last six years on three planning applications linked to Mr Campbell and Mr Fraser.

Mr Poots also confirmed that one of the schemes — a social housing project involving Mr Campbell — was granted permission despite local objections.

Emphasising that such approvals are not necessarily unusual, the minister said: “I have seen planning applications approved where there are over 1,000 planning objections from locals.”

In an interview with the Sunday Times last weekend, Peter Robinson said of Mr Campbell and Mr Fraser: “I have never tried to conceal the fact that these were not simply developers; they are friends. These are people that I have known for a very long period of time.

“In fact, in relation to Ken Campbell I have probably known him long before Iris was ever in politics and long before he was a property developer.”

He also said: “Never at any stage in my life have I taken any money from any businessman for personal advantage, never at any stage. Of course you ask people to go along to party fundraisers, we ask people to give support to the party when it comes to the elections and we have done that with hundreds of business people, maybe even more than that, over the years.”

The DUP leader further said that his party probably has the lowest amount of donations from the business community of all the political parties here.

“I don't think anybody will be able to argue that people have been giving money to the DUP because they are getting favours from it,” he added.