Coach Mark Petchey has joined Murray in Las Vegas this week

The 18-year-old Scot replaces long-standing British number one Tim Henman, who slips to third behind Murray and Greg Rusedski.

Murray moves up to 42 in the world after reaching the quarter-finals in Memphis last week and winning the San Jose title two weeks ago.

Rusedski remains 43rd, while Henman has fallen nine places to 49th.

Murray's move to the top of the domestic rankings ends Henman's seven-year reign as Britain's top player, but the Scot has played down the achievement.

I think it's great that Andy has been able to do as well as he has in such a short space of time Tim Henman

"It's not really that big a deal to be honest," said Murray.

"Obviously you'd rather be British number one than British number 20, but I'd much rather have a higher world ranking than British because you don't play any tournaments that are just British players.

"You're competing against the whole world and that's where you get your credit from the players from.

"If you're number one in your country it's obviously nice but it doesn't mean anything to the other players, whereas if you're in the top 10 in the world that's pretty special."

Henman told his website: "I think it's great that Andy has been able to do as well as he has in such a short space of time, and it's great for British tennis to have three players inside the top 50 in the world.

"Hopefully that will help inspire others to train just that little bit harder and believe that they can do it too."

Murray continues his season this week with an opening match against Tommy Robredo in Las Vegas, where top seed Andy Roddick has withdrawn because of "weariness".

This week's ATP men's rankings

Henman and Rusedski are in action in Dubai alongside Roger Federer, Rafael Nadal, Andre Agassi and a returning Marat Safin.