Olympic organisers are scrambling to quell a scandal over television images of half empty stands at the Games.
A government minister says an urgent inquiry has been launched to identify just who had failed to show up, and why.
Fans from all over Britain who were let down by a complex ballot system have been outraged by footage of empty seats at key venues.
Organisers say they are in touch with the International Olympic Committee to find out what happened, Reuters reports.
A Games official says it is still unclear whether the empty seats in several events, including tennis, swimming, gymnastics and basketball, were allocated to sponsors, international federations and athletes' families.
Culture Secretary Jeremy Hunt, the minister responsible for the Olympics, says he is disappointed by the empty seats and that the London Organising Committee is looking into it.
He told the BBC he thinks the empty seats belonged to sponsors, and says if they are not going to turn up, the seats should be made available to members of the public.
British Olympic Association chairman Colin Moynihan says one solution might be a 30-minute rule whereby fans would be allowed to take up vacant seats if spectators were late or did not arrive.