The Metropolitan Police force will face recruitment problems and have to pay more than �400,000-a-year for undercover police cars when congestion charging is introduced, a report has warned.

Under London Mayor Ken Livingstone's scheme, which starts on February 17, regular police vehicles are exempt or entitled to a 100% discount on the �5 daily charge for driving in to the city centre.

But the registration details of covert cars have to be kept secret so there is currently no way for undercover officers to get out of paying.

According to a report commissioned by the Metropolitan Police Authority, it is not possible to guarantee that sensitive details of unmarked police cars would not leak out when they applied to Transport for London (TfL) for an exemption or a refund.

Refund attempt

But there may be an attempt later, which TfL will support, to get a refund for hundreds of thousands of pounds after it has been paid out.

The report said: "There is currently no mechanism for obtaining an exemption or refund from TfL in these circumstances."

Congestion charging will also cost the Met an estimated �58,000 a year in administrative costs.

The force is introducing a six-week pilot scheme to pay the congestion charge for shift workers whose times of work mean they do not have easy access to public transport.

Response times

If this scheme is extended it will cost �713,000-a-year.

Not paying those charges for shift workers could lead to problems recruiting and retaining staff, the report warned.

The Met has said previously that the traffic scheme will help to reduce their response times inside the congestion zone.

But they say there may be an adverse effect to response times immediately outside the zone.