An angry Mr Hague telephoned Mr Portillo after he demanded the Tories give a stronger lead to the campaign against British entry to the single European currency. His intervention, in an article in The Daily Telegraph, was seen as a criticism of Mr Hague's leadership.
After Mr Hague's rebuke, Mr Portillo issued a statement praising his "bold leadership of the Conservative Party in general and in particular on European issues".
Mr Portillo said: "I am a strong supporter of all his policies, including those on Europe ... William Hague's leadership on this will bring about the revival of the party's fortunes and confirm his clear prime ministerial qualities."
The loyalty oath failed to stop another outbreak of Conservative feuding over Europe. Michael Heseltine, the former deputy prime minister, renewed his allegation that there was a plot by Eurosceptics to replace Mr Hague with Mr Portillo.
"I think William should be extremely concerned about what lies behind this Portillo agenda," said Mr Heseltine.
"It's quite obvious, when Michael comes back there is going to be a concerted campaign, in which newspapers like the Telegraph will play a significant part, in order to replace Hague with Portillo. It's as clear as any political event in the future ever can be."
Mr Heseltine warned that the Tories were heading off in a false direction. "The party's support is haemorrhaging from people who left the party to vote either Labour or Liberal, both of whom had a pro-European policy stance," he said.
Although Mr Hague's allies were playing down the affair last night, they were privately seething. "Portillo's criticism is bizarre," said one.
"We have given priority to the single currency issue by balloting party members on it. Others have criticised us for giving it too much priority."
Mr Portillo, who lost his Enfield Southgate seat in last year's general election, wants to return to the Commons in a by-election. But yesterday's controversy shows that his attempted comeback will be fraught with difficulty and strain his relations with the Tory leader.
Mr Portillo was rebuked by Michael Ancram, the Conservative Party chairman, who insisted: "We are giving a clear lead on the single currency. What we are looking for is for others to follow that lead."
Rejecting the criticism of the Tory campaign on the euro, Mr Ancram said: "We will be looking to bring people from business in. We will try and form a broad coalition, and we will be at the forefront of the argument."
In his article, Mr Portillo said the Conservative Party was the only body with the political weight and experience to lead the many organisations opposing the single currency. "Until we provide that leadership, there is a real danger that the majority against joining EMU will be whittled away by Gordon Brown's inglorious, but corrosive, argument that British membership is inevitable."Reuse content