The prospect of a rebuilt Wembley as England's new national sports stadium is not yet a "done deal", according to government trouble-shooter Patrick Carter.

The Football Association announced on Wednesday that Wembley is its preferred option, and that the details of the deal should be in place by April.

But in his interim report, Carter stated that a great deal of work still needs to be done before agreements guaranteeing the construction of the stadium can be signed.

"I believe we now have the prospect, but not yet the certainty, of delivering a national stadium at Wembley," Carter stated in his report.

Carter was appointed by the government in June to carry out a review of the national stadium project.

And he has recommended that the Birmingham option should "be actively considered" if the final contract for Wembley is not signed within "a reasonable timescale".

"There remains much to be done and I would counsel all concerned not to consider this a done deal until such time as legally-binding agreements are signed, at which point I propose to deliver my final report."

Carter rejected the Coventry City Council plans, stating that the �470m scheme was not supported by a business plan and had no costed design or commercial funding proposals.

Birmingham's proposal was described as "impressive", although Carter identified a funding gap of between �43m and �163m.

Carter insisted that the original plans for Wembley were "too expensive, the income stream too insecure and the management unconvincing".

The revised scheme is more modest and is underwritten by income from premium seats and a more realistic level of debt.

Next stage

"These changes bear out the wisdom of commissioning a review and not proceeding with the original scheme, that all parties now recognise was flawed," the report stated.

The report also highlighted the importance of clarifying the responsibilities of the various agencies involved in the decision-making process.

"A successful project must begin with a clear understanding of the respective commitment of the FA, government and Sport England," he said.

"This next stage will be complicated, with many interdependent contracts, and it will take some months to work through all the details and resolve outstanding issues."