HARBOUR Law caused a massive upset to win a dramatic Ladbrokes St Leger, with hot favourite Idaho unseating Seamie Heffernan when slipping with more than three furlongs to run.

Victory gave Laura and Ian Mongan's 20-strong dual-purpose stable a fairytale success and a first Classic triumph for an Epsom-based yard since Right Tack won the 1969 2,000 Guineas.

Sent off at 22-1, Harbour Law looked to have a mountain to climb on ratings, but the Queen's Vase runner-up took his form to a new echelon as he swept down the outside to give Mongan a first success at Group level and a dream Classic victory.

Harbour Law, owned by Jackie and Nick Cornwell, was tracking favourite Idaho towards the rear of the field as the runners galloped past the four-furlong marker with the race's complexion about to change dramatically.

Heffernan was inching Idaho away from the rail in preparation to launch the favourite into contention when he appeared to take a false step. Taking a noticeable stumble, Idaho managed to stay upright, but that could not save Heffernan, who was catapulted high out of the saddle and crashed to the floor, sending their Classic hopes up in smoke.

Up front, champion jockey Silvestre de Sousa took the race by the scruff of the neck on Ventura Storm, sensing a first Classic success of his own.

He was chased hard by Idaho's stablemate Housesofparliament and the winner looked sure to come from this duo with less than a furlong to run.

But George Baker, himself a Classic virgin, had timed things to perfection on Harbour Law and, although the eventual winner threatened to hang in behind the leaders, Baker got him organised and lunged at the leaders to score a remarkable win.

"That was brilliant. He's a classy horse, but it was a bit of a shock still," said Laura Mongan, whose biggest win before last Saturday came when First Avenue won the Imperial Cup over hurdles at Sandown in 2013.

She added: "He was obviously good enough and I am so glad we came here. He has proved he can do it. I was scared the whole way through the race because it is not particularly how we wanted the horse ridden, but George knows him and George did the right thing, all credit to him.

"It was a really professional performance from the horse. We knew he was going to go somewhere in life and he has.

"It proves that we can do it with the right ammunition. We do very well as a team with what we have got at home. It is great to get a horse like this and have a chance to bring him here for a race like today."

Harbour Law had three-quarters of a length to spare over 14-1 shot Ventura Storm at the post, with Housesofparliament a further short head away in third in a captivating finish.

"I promise you, I can't believe it," said a shell-shocked Baker. "I'm so happy for Ian and Laura. They had so much belief in him, have done everything right with the horse and they really deserve it. This is a sweet, sweet result."

For many northern trainers, the Western meeting up at Ayr this weekend is as important as any during the calendar year.

Yorkshire trainers have a great record in tomorrow's feature race, the Ayr Gold Cup, and they are again well-represented in the six-furlong handicap.

Richard Fahey has booked Graham Lee to partner the favourite Growl, while Bryan Smart is set to saddle Nameitwhatyoulike, so impressive in Listed company at York on his last start.

Closer to home, there is a competitive card at Catterick tomorrow, with the first of seven races due underway at 2.25pm.