INDEPENDENT gas supplier Calortex claims fewer domestic customers are switching from the incumbent monopoly provider in Scotland than in those UK regional markets liberalised earlier because of ''slightly anti-competitive'' behaviour by Scottish Gas and parent Centrica.

But Scottish Gas, which has ploughed resources into major advertising campaigns and has just announced a #3m, four-year sponsorship of the Scottish football team, claimed it was ''a nonsense'' for Calortex to claim a lack of proper competition.

Neil Lambert, Calortex's commercial director, produced industry figures showing that the new entrants' combined share of the domestic gas market in Scotland and the north-east of England had risen rapidly at first but levelled out at about 20%.

In south-west and south-east England, the first two areas to see the domestic gas market liberalised, the new entrants' share rose above 25% before reaching a plateau.

Lambert admitted that Calortex, owned by Dutch utility Nuon, Texaco, and Calor Gas, had not done as well as it had hoped in Scotland and the North-East, having secured only slightly more than 60,000 of 2.5 million potential customers.

Lambert said about half of all Calortex's initial supply contracts had been negated by ''objections and rejections'' by Scottish Gas and British Gas because these customers owed them money.

Lambert said that, though legal, this was a ''new phenomenon''.