The new shadow Chancellor, Mr Michael Portillo, yesterday returned to the political frontline with an attack on the European single currency.
He told BBC Radio 4's Today programme his beliefs on the euro were "entirely consistent" with Mr Hague's policy of not joining within the next parliament.
But he added that the task of creating a single exchange rate and interest rate for Europe would mean that "that exchange rate will almost certainly not be right for Britain most of the time".
He said that there were obvious constitutional and political consequences for Britain of joining the euro, which he said the government was trying to deny.
And he added: "People who favour the euro say that these constitutional implications can be handled, that they are not as important as we think they might be.
"What William Hague has said - with commendable modesty - is, `Alright, I am prepared to believe that one day you might be able to resolve these problems. I can't see how you could, but what's for sure is that all these problems couldn't be sorted out in the coming Parliament.'
"The proper position is for us in the next manifesto to be against the euro, so that people know that if they want to save the pound, there is only one way to do it and that is to vote for the Conservative Party."
In the interview Mr Portillo also said that he had not been lobbying for a shadow cabinet post. But he added: "I have been building up quite a friendship with William Hague over the last few years. It has been a strengthening relationship.
"In that sense, I am obviously pleased but perhaps not quite as surprised as some other people."
He also insisted he was "fully on board" with Mr Hague's promise to cut taxes while increasing spending on public services in the next Tory administration.
Mr Portillo added: "When the economy is growing, why does the Government feel that it has got to help itself to the same proportion of the increase in wealth and take more money out of people's pockets? If you have a government that is careful with taxpayers' money, that won't happen."