The upkeep of the bridge is paid for by tolls alone

The toll rose by 10 pence to 30 pence in 2003, but the bridge trustees say the new rise is necessary because of "unforeseen higher running costs".

Before the rise can be implemented for the 140-year-old bridge, the trustees must get the support of both Bristol City and North Somerset Councils.

Drivers will be able to opt to buy 1,000 crossings in advance at discount.

This latest increase has been prompted by a rise in overheads due to three main factors:-

The vaults

In 2002 a honeycomb of 23 vaulted chambers linked by shafts and tunnels was discovered within the stone supports of one of the towers of the bridge. Previously it was thought the 110 ft structure was solid.

Insurance

The cost of insuring the bridge doubled in 2003 and further increases are expected.

Illuminations

The lights on the bridge which first appeared in 1864 are due to be replaced. The trustees say a six-figure sum must be found if new lights are to be in place for the bi-centenary of Brunel's birth in 2006.

"It would be irresponsible to plan to run the bridge at a loss and spend our reserve funds," said Dayrell McArthur, chairman of the trustees.

"The bridge is run by a charitable trust. We receive no outside help towards our costs, either from central of local government or from lottery funds, therefore the bridge has to be paid for through tolls alone."