The British Horseracing Authority said on Sunday it will look at its procedures for declaring races void in the aftermath of the London National at Sandown Park on Saturday, when an extended delay for a stewards’ inquiry into the race meant many punters who were due a refund on their stakes had already left the course when the decision was announced.

Venetia Williams’s popular chaser Houblon Des Obeaux, the winner of three races at the track, suffered a fatal heart attack approaching the end of the first circuit in the race. As vets and track staff attended to the stricken horse on the racing line, the decision was taken to stop the race.

A member of the ground staff waved a yellow “Stop” flag, warning jockeys to halt racing immediately, as nine remaining runners approached the third last fence.

Two jockeys who were trailing the field – Aidan Coleman and David Noonan – pulled up but the remaining seven continued round the third-last and continued to race around the home turn and past the screens that had been erected around Houblon Des Obeaux.

A stewards’ inquiry was immediately announced and the seven jockeys that continued racing – Harry Skelton, Adam Wedge, Daryl Jacob, James Davies, Jamie Moore, Stan Sheppard and Philip Donovan, who was first across the line on Doing Fine – received 10-day bans for failing to stop, which threatens to rule them out of the busy Christmas programme.

Richard Hoiles, ITV’s commentator on the race, advised punters to “hold on to all tickets” in the expectation of a refund two minutes after Doing Fine crossed the line.

Bookies could not make refunds without official confirmation that the race was void, however, and that did not arrive until 4.15pm, 35 minutes after the flag was deployed.

Paul Struthers, the chief executive of the Professional Jockeys’ Association, said: “First and foremost, our thoughts to go out Venetia, her team and the owners and we shouldn’t let what happened subsequently make us lose sight of that.

“We will be lodging an appeal on behalf of all the riders who were suspended and it wouldn’t be appropriate to comment further until after that appeal has concluded.”

The BHA will not comment on the specifics of the incident until after the appeal but Robin Mounsey, their spokesperson, said: “Once the clerk of the course made the decision to deploy the stop race flag, the race will always be declared void.

“An inquiry was immediately announced and the jockeys involved and the clerk of the course were spoken to before announcing a decision, in line with procedures. In future, we will take a look at these procedures to separate out the void race part of the inquiry from the other elements, in order that we can inform racegoers, broadcasters and the betting public as to the outcome of the race more quickly.”

Min, the odds-on favourite at 8-11, took the Grade One John Durkan Memorial Chase at Punchestown on Sunday, but not without a struggle to hold off the persistent challenge of Hardline, a 25-1 outsider.

Hardline came with a strong run to head Min as they jumped the second-last but Min had regained a narrow lead at the final fence and he stayed on well from there to win by two and a quarter lengths.

Presenting Percy, who was making his first start since finishing eighth when favourite for last season’s Cheltenham Gold Cup, was third at 10-1.