Security raised as Wimbledon begins

Scotland Yard said changes had been made to policing plans for this year's tournament, with the UK's terror threat level at "severe", meaning an attack is "highly likely".

Extra officers will be on patrol - including some in plain clothes - and a "highly mobile" reserve unit is ready to respond to "emerging incidents", the force said.

It comes after at least 15 British holidaymakers were killed in the Tunisian beach massacre on Friday, with sources warning the death toll could double to at least 30, and as the UK prepares to mark the 10th anniversary of the July 7 bombings next week.

The tennis action on Centre Court kicks off today with defending champion Novak Djokovic's first round match, while 2013 champion Murray will begin his challenge tomorrow.

The Scot has been handed a tough draw as third seed, and may have to overcome former champions Rafael Nadal, Roger Federer and Djokovic if he is to achieve glory.

The British Association of Tennis Supporters have insisted Murray will have the full support of the Wimbledon crowd despite having voiced his support for Scottish independence in last year's referendum.

The Met Office has forecast glorious sunshine for the first three days of the tournament - with temperatures reaching 33C (91F) on Wednesday.

But spectators may need their umbrellas on Thursday when there is a risk of thunderstorms.

Bookmaker William Hill is offering odds of 11/4 for a Murray victory at Wimbledon, while number one seed Djokovic is the 11/8 favourite.

Federer, a seven-times Wimbledon champion, is a 7/1 shot, while Nadal, who is seeded 10th for the championships, is 20/1 to win.

In the women's draw, five time-Wimbledon champion Serena Williams is the 7/4 favourite, ahead of defending champion Petra Kvitova at 7/2.

Former players have hailed Murray's form since he married his long-term girlfriend Kim Sears in April.

The British number one declared "marriage works" last month as he won his second clay court title in the run-up to the French Open, where he eventually reached the semi-finals.

And he secured his fourth Queen's title to join the likes of fellow-four time winners John McEnroe, Boris Becker and Lleyton Hewitt.

A second Wimbledon title would add to Murray's already glittering career, which includes an Olympic gold medal from London 2012 and a US Open title.

The 28-year-old will be coached by the heavily pregnant Amelie Mauresmo for a second time at Wimbledon, alongside new recruit Jonas Bjorkman.

The All England Club will award a total of £26.75 million in prize money to competitors at the championships.

The gentlemen's and ladies' singles champions will each receive £1.88 million, a 7% increase on last year.

The queue for tickets started at 8am yesterday.

Stella Riley, from Wimbledon, was at the front of the queue for Centre Court tickets as thousands of people waited patiently before the gates opened this morning.

The Novak Djokovic fan, who had been camping out since 7.30am yesterday, before the official queue opened, said she was not put off by the UK's "severe" terror threat level.

Ms Riley, who is in her 60s and originally from Ireland, said: "I've been coming nearly every year for the last 30 years.

"People said be careful but it didn't cross my mind at all.

"I've always loved tennis, it's always interested me since I played as a young girl."

Organisers said the queue was at full capacity at 8am this morning, two and a half hours before the gates opened.

Michael Slatcher and his girlfriend Jenny Crockford were sixth and seventh in the queue.

Mr Slatcher, 32, from Ash Vale in Surrey, said he did not think Murray's support among English fans would be dented after the British number one backed Scottish independence.

"He's very Scottish but he's also very British," Mr Slatcher said. "He's always said he's very British. He works hard for the Davis Cup team."

Mr Slatcher said he had been coming to Wimbledon for the last 17 years.

"I used to tell school I was sick then I would appear on GMTV," he joked.