Shadow foreign secretary William Hague has said the new Conservative Party leader David Cameron deserves the help of old timers like himself.
William Hague says it is a rare moment for the Tories
Mr Hague said it was a "rare moment" for the Tories and said everybody needed to get involved.
The ex-leader is returning to frontline politics for the first time since 2001. Iain Duncan Smith and Ken Clarke are also to head up new Tory task forces.
Mr Hague began his job by attacking Tony Blair over the UK's EU rebate.
And he said the Tories had to make clear the mistakes made in the Iraq war, although the UK should not pull out its troops if it meant leaving Iraq in chaos.
Mr Hague joked that he must be mad to return to the fray.
"I think it is a rare moment in the Conservative Party," he said.
"I think David Cameron has the most fantastic potential as leader of the party. And I think he deserves the support of everybody else. He deserves the old-timers like me getting involved again and helping him out."
Mr Hague said the Tories could now form a team which looked like it could run the country.
"We have struggled to do that at times in recent years," he said.
The Save The Pound campaign against adopting the euro was a central plank of Mr Hague's 2001 general election campaign.
But the former leader denied being a hard liner on Europe, saying opposition to joining the euro and further European integration was now a common position for most MPs.
He attacked Tony Blair's negotiations over the European budget rebate, which continue on Thursday.
"I think that to give up part of the rebate with no concessions in return on the Common Agricultural Policy (CAP), in defiance of everything the government said until a few weeks ago, is a great mistake," he said.
Mr Hague said he was not saying the rebate should be the same forever but ministers had been wrong to abandon their previous insistence that there would only be change in return for reform of EU farm subsidies.
"They have now managed to give away that position while simultaneously alienating the countries of eastern Europe, upsetting the European Commission and getting nothing from the French," he argued.
Mr Cameron has pledged to take Tory MEPs out of the European People's Party (EPP) grouping at the European Parliament.
He says his party should not be allied with European federalists.
Mr Hague said the Tories would stick to the commitment to pull out of the EPP but there would be months of talks to try to create an alternative grouping of MEPs.
On Iraq, he said the UK had a long-term commitment.
"To pull out and leave the situation in chaos would be cataclysmic and a complete abrogation of our responsibility," argued Mr Hague.
He said the Conservatives should be clear with the US Government about mistakes made in Iraq.
He admitted a "spat" had opened up between the White House and Michael Howard but insisted there had been no major breach between British and American conservatives.