In a speech at the Carlton Club in London, Britain's senior European Commissioner said criticism of the EU by the Conservative leader last week did not stand scrutiny.
"Let us not be sidelined by a shrill and emotional reaction to economic and monetaryunion. It is both a logical extension of the single market in Europe and a natural complement to everything the Conservative party has stood for in the last two decades," he said.
In Fontainebleau last week, Mr Hague said the EU was a 50 year-old solution to post-war problems which was not necessarily applicable to the future. It had been set up for six member states and its structures might not be suitable for further enlargement.
Last night Sir Leon, who was delivering the RA Butler Lecture, accused Mr Hague of characterising the EU as "corporatist, state-centred and high- spending". His party leader's view seemed to assume that member states were to be forced into a strait-jacket causing serious social unrest, he said.
"I strongly believe that the characterisation of the European Union in these terms is a fundamentally flawed anachronism itself. In many ways, William Hague is applying a 1980s' vision to a simplified caricature of the European Union of the 1970s. It is not Europe that is out of date, but the perception of what is actually happening in Europe today," he said.
Sir Leon argued that EMU would be a great vehicle for the export of Conservative economic policies such as fiscal discipline, privatisation, deregulation and liberalisation.
"Why is it then, that it is precisely the party which was at the forefront of these policies, and indeed invented them in many cases, which now seems determined to turn its back on its own greatest achievement?" he asked.
Last night a Conservative spokesman said the speech was made in Sir Leon's official capacity as vice-president of the European Commission, and not as a party member. Mr Hague would not be responding, he added.
"As a member of the Commission he is politically neutral and is not supposed to be biased towards any party. He is defining policy as the Commission would expect him to do," he said.
The spat is likely to continue next week when Mr Hague addresses a meeting in London of leading businessmen opposed to European economic and monetary union.
More than 100 senior figures from the world of business and commerce will be at the launch of an 80-page critique rejecting the single currency on economic terms. Mr Hague intends to put the political arguments against British membership of EMU.Reuse content