The Olympic Stadium will hold 60,000 after the Games but some athletics events will attract crowds in the hundreds. Photograph: Westfield Group/PA Wire/PA UK Athletics has admitted it will be almost impossible to fill the Olympic Stadium when it stages meetings following the Olympics. The main event, the two-day London Diamond League Grand Prix, attracts a 17,000 capacity crowd to Crystal Palace where it is currently held and some of the lesser meetings are likely to struggle to attract spectators. The next most prestigious events are the UK Championships, currently held at Birmingham's Alexander Stadium which has a capacity of approximately 8,000. Ed Warner, chairman of UK Athletics, a partner in West Ham United's bid, said those national championships attract a crowd "in the high single thousands". He acknowledged that the other athletics event on the list, which includes the English Schools championships, south of England senior and junior championships, and Newham and Essex Beagles' British Athletics League meets, will be watched in a mostly empty stadium. West Ham's bid to occupy the £496m stadium, incorporating a track permanently in place around the football pitch, succeeded crucially because of the commitment to 20 days of "top class athletics" per year. "'Top class' is not a technical term in athletics as 'first class' is in cricket," Warner explained. "By 'top class' we mean the two days of the Diamond League, down to championships for each major age group. Some will attract a significant paying public, others a smaller paying public. We will also be able to bid for major European and world championships." Explaining why it makes sense to have a 60,000-seat stadium for events watched by crowds in the hundreds, Warner said: "We have never argued that athletics makes the stadium commercially viable. But we want our athletes to aspire to run on the track in a facility of such quality, and the warm-up track underneath is also important. West Ham made the call that they can make the stadium work financially, and we were able to piggy-back on that." Retaining the track permanently, as urged by Lord Coe, was acknowledged by the Olympic Park Legacy Company to have been crucial in their decision to prefer West Ham's and UK Athletics' bid to that of Tottenham Hotspur, which argued that refurbishing Crystal Palace is a more sustainable option. Spurs have hinted in their reaction that they believe West Ham will not retain the track long-term, because their supporters will be far from the action, and the athletics will almost never attract a crowd. However, Warner said West Ham have agreed the track will be a permanent feature in the stadium's future. "We have a commitment to an IAAF category one facility, to be maintained in the stadium, for the duration of the lease," he said.