'Half-asleep' Constitution Hill survives a late error before sealing trainer Nicky Henderson's 10th straight win.

The first word was sorry. As Boinville's Nico walked down Constitution Hill along the champions' path, he was greeted by Jaydon Lee, the boy who looks after the superstar hurdler, and made an apologetic face.

Constitution Hill had just extended its unbeaten streak but, surprisingly, its tenth consecutive victory was not perfect. Drama seems to follow this wonderful animal and he proved it once again in the final stages of a race he had won a long time ago, much to everyone's surprise.

De Boinville had spent much of the Grade Two Unibet International Hurdle with his hands gripping his partner's bridle tightly, trying to keep his impressive power chained. He had overcome his obstacles smoothly and everything was going according to plan until the ninth and final flight.

For unknown reasons, Constitution Hill bulldozed through it, making a noise like thunder. For a split second, you feared gravity might take over, and a crowd gasped at the prospect of horse and rider going their separate ways, but quickly, you were back on your feet.

He got ahead in the shoot, beating Brentford Hope as easily by three lengths as the prohibitive odds of 1/12 suggested he would, but de Boinville did not enjoy that little episode and was quick to present an explanation to trainer Nicky Henderson and owner Michael Buckley.

“Everything went as planned except for the last one,” De Boinville said, explaining that the mistake would never have happened in a race with a faster pace. I was half asleep. If I had woken him up after the second to last one, he would have left. He was just doing everything so easily.

Constitution Hill (right, ridden by Nico de Boinville) almost threw away a dominant victory

And what a glorious sight it was. Here was evidence that you don't need a penny in a horse to invest in it. As Constitution Hill entered the parade ring about 15 minutes before the start, there was no vantage point available as die-hard enthusiasts and first-time visitors strained to see it.

Throughout the race, his gallop was rhythmic and his hurdle race precise. One jump, in the penultimate quarter in the shadow of Cleeve Hill, was all one could hope to see: De Boinville must feel like every day is Christmas when he lifts his leg to ride him.

That's why the last flight was so incredible, so out of character with everything that had happened before. Be clear: this is not a sign of some flaw that has crept into your makeup. Henderson, with a smile, suggested it was Constitution Hill's way of keeping us all on our toes.

“I had a horse, called Zaynar, who was beaten 1/14 at Kelso a few years ago,” Henderson said, emphasizing that nothing can be taken for granted.

“I wouldn't have thought there were that many around here at that price, except Arkle (1/10 in the 1966 Gold Cup).

“It's a good idea for him to get that out of the way before the big event in March, right?” He just wasn't doing much, was he? It was just a little boring.

“I wouldn't say he was getting arrogant, but it was like he was saying, 'Ok, so what are we doing?' It's just taken a good turn.

Constitution Hill suffered a late error but steadied itself for a 10th consecutive victory.

Trainer Nicky Henderson (pictured) was delighted to see Hill continue to assert his dominance.

Henderson is now counting the days until Constitution Hill attempts to win back the Champion Hurdle he was unable to defend last year due to illness and who can blame him? Let's put it this way: If Constitution Hill lines up on March 11, its rivals won't see where it's going.

Henderson's name was chanted in the paddock afterwards, but the whispers from the rest of the card were for L'Homme Presse, who proved he is Britain's best hope for the Gold Cup in the Cotswolds Chase, and for East India Dock, who stood out in the Triumph Hurdle test.

“This horse is in good solid form,” trainer James Owen said. “I wouldn't change it for anything.”