From the Stop the War Coalition in Britain:
Stop The War Declaration To The New Prime Minister
We urge you on behalf of millions of British voters to:
1 Withdraw British troops from Iraq no later than October 2007.
2 Declare that this country will not participate in any attack against Iran.
3 Pursue a foreign policy independent of the administration of the United States of America.
Presumably, the new British Prime Minister will be Gordon Brown.
Tony Blair did a lot of damage to inner democracy in the Labour party, so it will be very difficult for the Left wing candidate John McDonnell to win the Labour party leader election.
If he does unexpectedly, there is a real chance that he will agree to the petition demands.
See also here.