Lewis Hamilton has admitted that Formula 1's new regulations will make it 'very tough' for him to repeat his drivers' world championship success in 2009 - as he evoked the possibility of a fourth team joining McLaren-Mercedes, Ferrari and BMW-Sauber in the title fight.

Having missed out on the ultimate laurels by just a single point at the end of his startling rookie campaign in the top flight in 2007, the British star triumphed by a similarly slender margin twelve months on, after overtaking Toyota's Timo Glock on the final lap of a nail-biting Brazilian Grand Prix at Interlagos last month to seal the deal.

In so doing, the McLaren star inscribed his name in the record books as the youngest driver ever to lift international motorsport's greatest and most coveted prize at just 23 years and 300 days of age.

He agreed, though, with the contention of McLaren team principal Ron Dennis that the radical cost-cutting measures being brought into force for next year and beyond - including longer-lasting engines, shorter grands prix, a ban on refuelling, curtailed in-season testing and cheaper, off-the-shelf engines for smaller teams - will make for a 'challenging period', as with the world's car makers reeling from the blow of the global credit crunch, the sport bids to prevent any more squads from following Honda out of the exit door.

"I don't think it will make it easier," the Stevenage-born ace is quoted as having said by the Associated Press. "With the new regulations it's going to make it very tough to win the championship again.

"We have less testing obviously, but I think we as a team are in a position to pull together and make a difference in some other way. Everyone's in the same boat.

"It's amazing how many different things happen in a year, but all we're thinking about is how we can continue in the sport and continue to put on a good show, how we can move forward and continue to win as a team.

"We don't know who's going to be quick; surely we're going to be at the front, with Ferrari maybe, BMW, but you never know. Maybe there's going to be a fourth team up there with us."

Should such a 'fourth team' indeed materialise, it is widely expected to be Renault, whose talisman driver Fernando Alonso notched up the most points of anyone during the second half of 2008, and whose progress over the course of the campaign unquestionably out-accelerated that of every one of its rivals.

Hamilton went on to add that it had been 'hard' to become F1's first-ever black world champion because of having 'to break down the barrier'.

"It wasn't easy but we got there," the nine-time grand prix winner mused, "and I have been accepted very well into the sport. Balancing increased commitments from sponsors, the media and fans was turning into the toughest part of the job.

"There are always going to be pressures there and it's how you deal with them; it's how you rise above it."