Thousand of tickets to watch synchronised swimming at the London Olympics 2012 were sold by mistake, after human error meant 20,000 was typed into the ticket data entry box instead of 10,000.

The Aquatics Centre event was not oversubscribed during the first round of ticket sales, but it was in was the second round of sales in July, meant to offer unsuccessful applicants a second chance, when the error was made.

London Organising Committee of the Olympic and Paralympic Games (Locog), responsible for the mistake, are now faced with the unenviable task of asking thousands to return their tickets.

Instead, ticket buyers will be offered spaces to see their second or third choice of event at the London 2012 Olympics.

Potentially this means that they could end up watching some of the Games' most high profile heats such as athletics or the swimming finals.

The upgrade not only offers ticket holders spaces at some of the Olympics most sought after events, but also offers a discount.

Many of the events that have been offered in exchange originally cost more than tickets to watch synchronised swimming in the first place. The cheapest tickets to the Aquatics Centre event were only £25, compared with the £75 tickets to the main stadium.

More than 3,000 buyers have already been contacted over the Christmas period to try and rectify the mistake.

A London 2012 spokesperson said: “As a result of finalising the seating configurations in our venues and reconciling the millions of Olympic and Paralympic ticket orders against the seating plans for around 1,000 sporting sessions, we have discovered an error in seats available in four Synchronised Swimming sessions.

"In December we contacted around 3000 customers who had applied for tickets in the four sessions during the second round sales process. We are exchanging their synchronised swimming tickets for tickets in other sports that they originally applied for.”

The synchronised swimming ticket error comes as fresh embarrassment to Locog. The Olympics coordinator came under fire last year, after the ticket selling site crashed as thousands logged on to reserve a space at their event.

People will be able to sell their unwanted Olympics tickets on Friday 5 January.