Harbinger has powered his way to the title of top-rated racehorse in the world thanks to his breathtaking performance in the King George VI And Queen Elizabeth Stakes.

Racing's official assessors had no problem in raising the Sir Michael Stoute-trained colt forward from a mark of 123 to 135 following his 11-length romp in Ascot's midsummer showpiece on Saturday.

"You've got to be very impressed. He looked an improving colt before the race," Phil Smith, the British Horseracing Authority's head of handicapping, told At The Races.

"All his performances this year were very progressive and I expected him to a run a big race. I didn't think he'd win and I certainly didn't think he'd win like that.

"We looked at the second horse, Cape Blanco, and imagined what if Harbinger had not been in the race. Cape Blanco was 119 going into the race and so we took the view that Cape Blanco had replicated his 119.

"We therefore just had to decide what we called the 11 lengths. We took the view that was worth 16lb, which would be pretty much the norm and brings Harbinger out on 135.

"It's quite a big jump - we had him on 123 before that - but I'm pretty confident he's that and could probably be better. It was very impressive."

He went on: "Instantly we've got Harbinger 1lb below Sea The Stars' end-of-season performance (in the Prix de l'Arc de Triomphe). He has still got one, two or possibly three more races to come, so we will see how he runs in his subsequent races.

"It may well be we have him as high or higher than Sea The Stars. He's the best horse in the world today, definitely, but he's not the best horse ever. He's got a hell of a lot to prove.

"It was a once performance. No-one could get any of his previous performances into the 130s, even though he looked to be climbing the ladder. We would want him to do it again before we can get him into the late 130s or early 140s. He's got to do something similar in the future."