Due to a regulation change in the Swiss market, William Hill reached out to its Swiss players on Tuesday to inform them all ante-post bets are to be voided.

However, Gambling Insider understands the operator will be refunding around 400 bets in total.

A Swiss player had staked €1,500 ($1,705) each way on Ashleigh Barty to win the women's singles at Wimbledon at 33-1, who is now as short as 7-2 to win the tournament.

The operator’s Communications Director, Ciaran O’Brien, exclusively told Gambling Insider all players would be refunded to the appropriate cash out value if they were sitting on a profit, rather than just receiving their original stake back.

All other bets placed will be refunded at their original stake. Other bookmakers operating in Switzerland are expected to follow suit.

O’Brien said: “All customers will receive refunds, or if they are sitting on a major price change we will refund them at the latest cash out value, even if there’s no cash out market.

“A vast majority of the bets will be sitting at a lower cash out, so a refund will be better for them. We are currently manually going through the bets now and refunding all customers.”