A Home Office source has said that the government will have to pay "tens of millions" for a new radio system that allows Metropolitan Police officers to communicate on the London Underground, according to the Financial Times.
The comment puts a spotlight on Airwave, the police radio system being developed in partnership with mobile operator O2 and provided under a controversial Private Finance Initiative.
A separate contract called Connect has been developed for London Underground but cannot be used by the Met.
London Underground is drafting a variation to the Connect contract which will allow the Met to use the service, for which the Home Office is expected to pay.
However, London Underground has been in talks with O2 for almost two years to modify the Connect contract so that police radios can work underground.
The original contract, due for completion this year, has attracted criticism because it cost £1.2bn and is two years behind schedule. Airwave has already cost almost £3bn.
The issue has received considerable attention since the shooting of Jean Charles de Menezes at Stockwell tube station during the London bombing campaign in July.
It has been widely reported that firearms officers involved in the shooting lost contact with their superiors as soon as they went underground.
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