A Commons debate on impeaching the prime minister could take place early next year as the MPs behind the attempt said they have gained support from all parties.

So far they have secured the backing of 21 MPs, including the former Labour defence minister Peter Kilfoyle, the former Conservative Foreign Office minister Douglas Hogg QC and the Lib Dem MP Jenny Tonge.

By January they hope to secure 50 supporters to revive the antiquated parliamentary device.

The campaign has received added impetus from the UN secretary general Kofi Annan, who declared the US-led invasion of Iraq illegal earlier this week.