Cash needed to keep Medway Tunnel open could run out within six years.

That was the stark admission made by Robin Cooper, the council’s director responsible for roads.

Speaking at a full meeting of Medway Council he said: “I cannot give any guarantees beyond 2015.”

The council agreed last year to buy the tunnel from its owner, the Rochester Bridge Trust.

At a sale price of just £1, the tunnel might look like the bargain of the century.

The Bridge Trust has also pledged to give the council £3.64 million towards maintenance costs.

But, even with other promised cash, there are fears among opposition councillors the cost of running the tunnel will be a crippling burden on Medway’s finances.

The council is nevertheless pressing ahead with a bid to buy it outright from the Rochester Bridge Trust and to get the government to fund it in the future.

Mr Cooper told Labour group leader Cllr Paul Godwin: “Our best estimate is that the money we get from SEERA (the South East Regional Assembly), plus money from the Bridge Trust, the council and from our transport plan should be sufficient to fund the tunnel until 2013 to 2015.”

Mr Cooper said the council was lobbying Parliament through Medway’s three MPs (two of whom are government ministers, and one – Gillingham MP, Paul Clark – is roads minister).

He said: “It is a unique tunnel. The government treats it simply as 725 metres of Tarmac. There is no government funding for the tunnel structure.

“We still think this is the best deal for the council.”

The bulk of the additional funding, £5 million, comes from the regional assembly (in which Medway is the only non- member council) using cash not spent by other councils.