The cost of the 2012 Olympic aquatics centre has risen, but savings made elsewhere could see a final overall budget underspend of up to 500 million pounds ($807.9 million), government figures showed on Tuesday.
The wave-shaped venue, designed by Zaha Hadid, is expected to need an extra 11 million pounds to keep construction on track after problems with the roof and to meet strict poolside air temperature guidelines, the latest quarterly figures showed.
The cost has been on the rise since the original estimate of 75 million pounds, and now stands at 268 million pounds.
But the overall Olympic bill is expected to stay within the 9.3 billion pound budget, with the share of the Olympic Delivery Authority (ODA) -- the body responsible for getting the Games ready -- expected to come in at 7.23 billion pounds.
"The ODA has continued to drive down costs and deliver savings despite this being the most complex year in construction terms," said Olympics minister Hugh Robertson.
The ODA has made 750 million pounds of savings since the 2007 baseline budget was agreed, including 29 million in the last quarter, the bulk of which was in response to the government's October spending review.
Part of the savings came from ditching the 7 million pound eye-catching plastic wrap around the main stadium, a move criticised in some quarters, including by the architect.
But Olympic officials suggested alternative funding could be found to restore the wrap, with "real possibilities being explored".
"As soon as we were clear that this wouldn't affect wind speeds and timings in the stadium then we were happy to take it (the wrap) off and then open it up to architectural experts and others who will take a view, and indeed sponsors, and the private sector in general to see if they want to have a look at it," Robertson told reporters.
A performance-related payment of 10 million pounds was put aside for the ODA's delivery partner, the CLM consortium.
The contingency fund stands at 1.14 billion pounds, with about 500 million pounds earmarked for venue security and ferrying people safely between transport hubs and venues and other measures.
The remaining 500 million would be used for any unexpected costs, but potentially could be banked by the Treasury as a saving.
But the final cost would still be considerably more than the estimated 2.4 billion pounds announced when London successfully bid to host the Games.
The Olympic Park in Stratford, east London, continues to take shape, with 75 percent of it completed. The velodrome is due to be the first new stadium completed early in 2011.