Reverse exhibitionists are known to draw attention to themselves through their very reclusiveness. Lawrence of Arabia was a prime example; some would say that the Barclay brothers exhibit symptoms of the same syndrome.

There Sir David and Sir Frederick Barclay sit in the mock gothic castle that they built on the tiny Channel island of Brecqhou, counting their £650m fortune amid opulence worthy of Roman emperors and willing to go to extraordinary lengths to protect their privacy. This secretiveness has inflated their status to mythical proportions.

However, last week the 69-year-old twins blew their cover by emerging from the shadows with an audacious deal to take over The Daily Telegraph and The Sunday Telegraph that left rival suitors fuming. After years of repelling boarders, these ideological fans of Margaret Thatcher had opened their castle doors, albeit briefly, to an interviewer from The Guardian.

Perhaps the gesture was an acknowledgment that if their £260m bid to secure control of the Telegraph newspapers from the embattled Lord Black succeeds — and they admit it is risky — they will become public figures in a way that they never were as owners of The Scotsman, The Business and the defunct The European.

Few of their friends are willing to speak on the record but this description by one is notable: “They are quite different. David is the front man and Freddie hardly speaks.

“When they are together they defer to each other all the time. They have a warm relationship with no tensions. They are mirror twins: if you look at one, the other is a reflection. One has a parting on the right, the other on the left. I think they are mirror twins in personality, too. David is basically optimistic whereas Freddie is fairly pessimistic. They act as a clever duo because they take opposite points of view all the time.”

They are already learning the perils of breaking their Trappist code of silence. On Monday David Barclay told The Guardian that the Telegraph papers would “certainly not” be the house organ of the Conservative party. Performing a U-turn the next day, he said that the paper’s editorial position would remain unchanged.

The brothers have enjoyed good relations with both the Tories and Labour. They were so taken with Thatcher that when she had left Downing Street and expressed a liking for a Belgravia home that they had sold, the twins bought it back and sold it to her for the price they had originally asked for it. Under Labour they were knighted in 2000.

It has been a momentous week for the twins. First they went hunting for Hollinger Inc, Black’s Canadian company that controls 73% of Hollinger International’s voting shares. Besides the Telegraph newspapers, this could produce £1 billion. Then on Thursday, to widespread surprise, the government gave the green light to their £590m purchase of the mail order business previously owned by Great Universal Stores, giving them 75% of the market.

Charles Garside, who as editor of The European from 1992-97 had “hundreds” of meetings with the Barclays, found them “charming” hosts and “fascinating” conversationalists. He avers that the brothers were “hands-off” proprietors and that Telegraph staff should count themselves “extremely lucky”.

However, another European employee recalls that the brothers discouraged any negative articles about Monaco, where they are partially based.

Somebody who dealt with Frederick, reputedly the gentler twin, said: “He struck me as being very charming and ruthless. And he would cut you dead if it wasn’t working out. You detect the steel there.”

Others are mystified by the brothers’ modus operandi. Philip Beresford, who compiles The Sunday Times Rich List in which the Barclays rank jointly at 34, says they are the most difficult of the list’s 1,000 entrants to value.