REPAIR work will be carried out on the Thames Barrier after London's main flood defence was discovered to be leaking.
Officials at the Environment Agency have already employed consultants to check out leaks in the £500 million barrier's concrete piers.The repair work is now being costed out before contractors are brought in to fix the problem.
An agency spokesman said: 'Radar surveys of the concrete have recently been completed and a presentation was made at the Thames Barrier last month.
'The report confirmed there was water ingress through the concrete and the route by which it is getting in was also identified.
'The problem is not considered to be serious but contractors have been asked to supply a costing for implementing repairs to one pier.Once costings have been received this will be evaluated.'
The problems are on the giant 50 m underwater concrete piers, which are built 15 m into the riverbed.
The piers house steel shells that are hydraulically raised whenever the capital is on flood alert.
A source close to the project said: 'There has been a problem with water ingress for some time and previously it was just pumped out from the piers.
'The ingress has been increasing and some repairs were carried out but they failed so a survey has been carried out to discover the extent of the problem.
'There's no problem with the barrier itself.That is fully functional. It's a question of some leaking in the seals between blocks of concrete in the piers.'
The Thames Barrier took eight years to build between 1974 and 1982. It was designed by High-Point Rendel.
The agency spokesman said: 'Since then the barrier has been used on 88 occasions for flood defence purposes.
'During this period some minor seasonal leakage has occurred in the joints of the concrete piers that house the main barrier-operating machinery.'