A row has blown up over plans for a motor racing circuit in Wales, with Silverstone claiming it could be being funded by illegal state aid.

Silverstone Circuits Limited has written to Prime Minister David Cameron asking for clarification of financial support for the Ebbw Vale Circuit of Wales project.

There have been reports that public money of up to £50 million could be put into the circuit, possibly via the Welsh Assembly.

However, a statement from Silverstone said its bid for financial support to secure the future of Formula 1's British Grand Prix was denied on the basis that this would be classed as illegal state aid.

"Silverstone has been advised that an injection of funds by the Welsh and/or UK governments to the Circuit of Wales project could also amount to illegal state aid, as a transfer of state resources would give Circuit of Wales an economic and selective advantage over other circuits (and developments)," said the statement.

"There are currently a number of well established, privately funded circuits in the UK, including Wales, that feel that the British motor sport industry would be threatened by the addition of a government-funded circuit.

"Silverstone has no objection to competition between UK circuits, but it has to be a level playing field.

"Silverstone reiterates that it is sympathetic to the economic situation in Ebbw Vale, but motor sport at circuit level is not particularly profitable and is often loss-making. Many UK circuits are under-utilised and struggle for revenue. It is unrealistic to suggest Circuit of Wales will be the exception."

Planning issues have delayed the start of work.