Irregular betting activity surrounding the Scottish Premier League match between Motherwell and Hearts last night is being investigated by the Association of British Bookmakers.

The ABB was alerted after a new customer in the Liverpool area placed an online single bet of £500 on there being a red card during the game at odds of 10-1. All bets on the same market are now being investigated. Motherwell's midfielder Steve Jennings, who is from Liverpool, was dismissed eight minutes before the end of Hearts' 2-1 victory for apparent dissent and placing a hand on the referee, Stevie O'Reilly.

Tom Kenny of the ABB said: "We have put an alert out on the Motherwell game and that is quite normal when a new punter asks for an unusual bet. We want to see if there is a parallel elsewhere.

"It is important to point out that something that is unusual is not necessarily suspicious and something that is suspicious is not necessarily fraudulent."

It is unclear which bookmaker took the £500 bet, at what is a generous price. William Hill offered 4-1 for there to be a sending-off in the same game and Ladbrokes 3-1. Betting exchanges are not involved, as they do not fall under the auspices of the ABB. Ladbrokes reported nothing suspicious but is still investigating.

Jennings had been booked earlier in the match but was shown a straight red card, with Motherwell officials explaining afterwards that the 26-year-old had asked O'Reilly to "stop cheating" his team.

Jennings, who will serve more than a one-game suspension after breaking through a disciplinary points barrier, has been receiving injections for a painful problem with a wisdom tooth. Motherwell had hoped the player would wait until the end of the season to have that tooth removed but the time he will now spend without a game means it can legitimately be taken out immediately.

A statement from the Scottish Football Association said: "Following information received from the ABB, we are aware of alleged betting irregularities surrounding a sending-off incident in the Motherwell v Heart of Midlothian match on Tuesday 14 December 2010. At this stage, we are not in possession of the facts regarding the allegations and are waiting for further information from the Scottish Premier League in due course. Once we are in possession of all of the facts we will be in a better position to provide more detailed comment on the matter.

"In the meantime, we will be working with our colleagues at the Scottish Premier League to establish the details surrounding this incident."

Motherwell said: "The SPL have confirmed to Motherwell Football Club that there is an investigation by the ABB surrounding last night's match with Hearts. There will be no further comment at this time."