A London assembly committee has warned that the capital's transport system will need improvement if a bid to host the Olympics is to succeed.

The culture and sports committee called on the government to adopt an all-or-nothing approach towards backing a possible bid to host the 2012 Summer Games.

The prime minister has also added his voice to the debate, raising the question of whether a bid could be successful if resources were committed to it.

The GLA members outlined the extent of transport improvements needed to win a potential bid, and they have called on the government to give whole-hearted support to the east London regeneration project.

The report says that with as many as nine million spectators potentially visiting the city, doubling London's population, a temporary road linking north and south London will be needed to enable athletes to move between venues.

The committee also recommends the appointment of an Olympic Transport Committee to help manage the increased use of public transport and an Olympics minister to oversee the development of the infrastructure.

Feasibility studies have also estimated that up to 11,000 athletes, 10,000 support staff and 20,000 journalists would attend the event.

The improvements required to cope with the influx could transform the city's ailing transport network, said the committee.

Meg Hillier, chairman of committee, said that transport would be the "key" issue if London is to successfully host the Olympic games in 2012.

"Major projects need to be started by the government as soon as possible if they are going to be completed on time," she warned.

"If the government decides to back a bid, we ask that it is bold in its support. A half-hearted bid will do no favours to London or the UK."

And she predicted that a united approach to a bidding for the Games would give London a "sporting chance" of success.

Asked on Monday whether he would like to see the games come to London and whether the government would support a bid, the prime minister responded that the likelihood of London hosting the 2012 games needed to be assessed.

"It would be great to have an Olympic bid, but the costs of that have been set out, whether it's affordable and so forth, I think the most important of those is are we going to have a realistic chance and prospect of winning," he said.

"That along with the other things is what we are looking at the moment. So we have to make sure of that before we OK a bid."

The PM did voice his support in principle for a bid, but with qualifications.

"If you could get the Olympics in London should you take it? Of course," he said.

"The question is will we able to do that? Is it likely that we will succeed? And that's the consideration we are giving it at the moment. But you've got to see whether it's affordable but also whether you've got a good chance of winning or not."

Ministers have spent the Christmas period studying reports on both the feasibility of hosting the games and the "winability" of any bid ahead of a final decision later this month.

Newspaper reports over Christmas suggested that the prime minister was veering away from the idea after lending his personal support to the failed football World Cup bid and the troubled millennium dome project.

The new Wembley Stadium building is also running late and over budget and the government does not want to have to underwrite any "blank cheques" for a successful Olympic campaign.

But Monday's newspapers hint that culture secretary Tessa Jowell may be supportive of the idea.

In a debate in the Commons chamber on Tuesday she is expected to tell MPs that there is a "very strong sporting case" for the capital hosting the games.