The cost of relocating the Thames Valley Police headquarters from Kidlington to Bicester will be more than 20m, a new report claims.

Thames Valley Police purchased land at Gowell Farm in Bicester in 1989 in the hope of building a new headquarters there. The existing site at Kidlington is seen as overcrowded, with a lot of money needing to be spent in the short-term to bring its facilities up to scratch.

The force and the police authority have always hoped the plan would be self-financing, with the sale of the Kidlington site and surplus land at Gowell Farm funding the new building, but a new report to the Thames Valley Police Authority's strategy, planning and finance committee said this is not guaranteed. The sale of the land is expected to raise 23m, but the cost of a new headquarters building with a control room is 25m.

The authority is now planning to modify the plans so that control rooms are located instead at Abingdon and Milton Keynes, bringing down the cost of the Gowell Farm scheme.

The information report to the committee, which met this week, said: "The total cost of the scheme which included provision of a control room is estimated at 25m. "It is now the intention of the authority to locate the force control rooms at Milton Keynes and Abingdon. If this element is removed from the Gowell Farm scheme this will assist by reducing construction costs and thereby increasing the prospects for the project to be self-funding."

Three planning applications one for the new headquarters and two for housing on the existing Kidlington site and on surplus land at Gowell Farm were submitted to Cherwell District Council last month.

The report also says the earliest possible completion date for the new headquarters would be mid-2004.