Rupert Soames, a grandson of Sir Winston Churchill whose family maintains links to the Tories, told peers "anyone who has dared open their mouths on the subject with views that are contrary to those of the SNP have brought down on themselves rains of bile and ire which are really unpleasant".
Appearing before the House of Lords Economic Affairs Committee, the Eton-educated businessman dismissed the benefits of breaking away from the UK as "small and tenuous" compared with the "large and serious" disadvantages.
He said: "A lot of the language is very intimidatory. I bluntly think that people think they have got better things to do than be hauled over the coals. I think that process will begin to change as we get closer to the referendum."
He said Aggreko, a Glasgow-based temporary power firm, would face "enormous additional complexity" from independence in the short term, and there was likely to be a permanent burden.