Williams sisters
Williams sisters Reuters

They are the most successful tennis-playing sisters in the world - but Wimbledon's former head racket stringer has branded the Williams sisters "horrible people".

In a frank, tell-all interview with The Times, Liam Nolan, who worked at the tennis championships for 20 years until 2002, pulled back the curtain to show the reality of the game's biggest stars.

He claimed Novak Djokovic had asked him for advice on how to pick up women and described Roger Federer as a boring man you "don't want to be stuck in a lift with".

Although he left the championship to found the UK Racket Stringing Association, Nolan remains a popular stringer and regularly comes face to face with the best players, who, he says, are quite different off court to their more public persona.

It was Serena and Venus Williams who prompted his most outspoken criticism.

He said: "I didn't like the William's sisters; they are horrible people. I remember we were raising money for a kid's hospice and we would have two T-shirts that we'd get all the players to sign and they were the only two who refused bacause they said they had not got enough time."

Nolan claims he is good friends with the Murray family and revealed that Federer likes to have the strings in his racket tied facing in a certain way. It is this obsession with the game that means he has little to talk about.

"[Federer's] happy to enjoy a coffee and sit down with you and not talk for half an hour. The players are really not that excuiting. They live in their own little world," he said.

Nolan said that players, particularly seven-time Wimbledon champion Pete Sampras, would ask for their strings to be changed soon before a match.

He said: "Even if they haven't used the strings in a racket theyll get the whole lot chopped out and start all over again. They need to feel confident that when they are out on court and a string breaks the next racket will feel exactly that same as the one that they have just been playing with."

Nolan praised Anna Kournikova's mother for insisting that she would keep her feet firmly planted on the ground, telling her to make tea for them all on one occasion.

He also said Djokovic and Janko Tipsaravic came to him during the Davis Cup asking where they could find women. He told them that they were wearing blue shirts in Glasgow on a Saturday and therefore had a "50-50 chance of getting stabbed".

Nolan is a Guardian reader, and wrote a piece about himself in the paper's Good To Meet You column in 2010. In it he revealed that he used to be in the RAF, which he represented in judo. He spent 27 years working for the prison service as a PE teacher.

He described being racket stringer at Wimbledon as "a good job, but there was a lot of politics, so I resigned".