An irreverent Boris Johnson has commended the British for exhibiting the politeness of hosts by not winning too many medals in the opening days of the Olympics.

At a surprise appearance at the beach volleyball in Horse Guards Parade, the London Mayor also had the crowd on their feet as he patented the "Boris wave".

He told the 15,000 spectators at the raucous venue that London was doing the Olympics proud.

"Everybody I talk to seems to be enjoying it," he said.

"The transport system is holding up very well and you know we have still got plenty of medals to win.

"I think we are showing great natural restraint and politeness as host nation in not hoarding the medals more so far."

His light-hearted address was well received in arguably the most colourful arena at the Games.

With pop and rock music ringing out between points and bikini and beach short-clad dancers putting on choreographed routines during breaks in play, beach volleyball is quickly laying claim to being the most fun sport at the Olympics.

Mr Johnson needed little encouragement to get the enthusiastic supporters pumped up even more when asked to start a Mexican wave.

But instead of triggering a domino effect around the stands, his initial effort prompted everyone to stand and throw their hands in the air at the same time.

"That's the first Boris wave of the Olympics," joked the stadium announcer.

After two more attempts, the mayor eventually got the more familiar Mexican variety in motion.

He joked that former prime minister Gordon Brown had only agreed to spend billions on the Olympics if he could be guaranteed a view of the beach volleyball from Downing Street.

While No 10 is close by, the mayor noted that unfortunately you could not see the action from there.

"Plus he (Mr Brown) is not here to enjoy it either, never mind," he quipped.

Mr Johnson said the Horse Guards Parade venue was "amazing".

"I think it's just unbelievable," he said.

"Who would have thought we could create an amazing arena like this in the middle of Horse Guards? This is totally wonderful.

"I would like to thank all the volunteers, everybody who has taken part in it, and I would like to thank the weather, thank the great British weather, for putting a cap on it all."