Parties fighting the London mayoral election have accused the government of introducing a controversial new procedure that will discriminate against smaller parties and independent candidates.

The government plans to scrap the traditional free mailshot for all parties running in the election, saying that it will cost too much.

It has also set the spending limit for the campaign at £1m, a figure opposition politicians say only Labour can afford.

Taking the unusual step of holding a joint press conference, the Tories, the Liberal Democrats, the Greens and the Electoral Reform Society all criticised the plans.

One went as far as to suggest that the move would prevent Labour MP Ken Livingstone running as an independent should he fail to win the party ballot.

The parties said that the proposals would leave Labour able to buy influence, while others would lose the usual means of contacting every elector in the capital.

Trouble ahead?

Liberal Democrat home affairs spokesman Simon Hughes issued a thinly veiled threat that the government could face stiff opposition in the House of Lords - where it does not hold a majority.

And speaking for the Conservatives, Bernard Jenkins, the party's new London spokesman following the defection of Shaun Woodward, said Labour was trying to rig the ballot.

"These proposals are arbitrary and unfair. There has been no independent scrutiny of them by any outside body such as they Neill Committee.

Labour acting without consensus

"There is not a shred of consensus between Labour or any other party for these plans," he added.

A mailshot for the capital would cost a considerable amount and would almost certainly be beyond the reach of most parties, and independent candidates.

When asked if he believed the plans could be part of an attempt to scupper the possibility of an independent Livingstone campaign, Mr Jenkins said it was "unlikely that if Ken were an independent he could find the money".

Green candidate Darren Johnson said his party would be hit hard by proposals which would cost "an arm and a leg".

He attacked the move as a "calculated attempt by the Labour leadership [to make] life for small parties and independents as difficult as possible".