Motoring groups have accused Gordon Brown of misleading drivers over increases in fuel duty after he reneged on a promise to spend the money on transport improvements.

In 1999, when Mr Brown was Chancellor, he said in his preBudget report: “If there are any real term rises in road fuel duties, the revenues will go straight to a ring-fenced fund for the modernisation of roads and public transport.” He repeated the pledge in the Budget the following year.

But last Monday’s 2p rise in fuel duty, despite being well above the annual rate of inflation, is going into the Treasury’s consolidated fund for general public spending rather than being earmarked for transport.

A Treasury spokesman said two further increases in fuel duty – 2p a litre next April and 1.84p in April 2009 – would also go into the fund.

He confirmed that since Mr Brown made the pledge, not a penny had been transferred into the “ring-fenced fund”. This was because fuel duty had been frozen for several years.

“By 2010, at the end of the fuel duty increases announced in the Budget, real fuel duties will be 11 per cent lower in real terms than they were in 1999,” he said.

Paul Watters, head of roads policy at the AA, said: “The public were misled into thinking that when they paid more at the pumps, the money would actually be spent on better transport.

“But by a sleight of hand, we find there is to be no special fund at all, despite three successive years of significant increases in duty.”

He said that motorists paid about £45 billion a year in various taxes but only £7 billion was spent on roads.

Theresa Villiers, the shadow transport secretary, said: “This is a blatant broken promise which Mr Brown is trying to explain with a tortuous reinterpretation of what constitutes an increase in duty.”

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