UK and German mobile telephone operators were simultaneously raided last night by the European Commission as part of an investigation into price-fixing.

A total of nine companies were raided, including the four biggest operators, Vodafone, Orange, BT Cellnet and One2One, after an 18-month investigation into consumer charges for international roaming.

In its statement, the EC said its initial enquiries had "established serious competition concerns that warrant further investigations."

British consumers are currently being stung with charges of £1.99 a minute to make calls while they are abroad and £1.49 to receive them - a sum 10 times higher then those experienced by US users.

The commission said it wanted to see whether there was any evidence of "collective fixing of consumer retail prices by mobile operators in both countries" and "whether German operators have illegally fixed the wholesale prices they charge."

Mario Monti, the EC's competition minister, expressed his concern over price-fixing earlier this year, stating current retail charges "show an almost complete absence of competition with high and rigid prices."

Vodafone and One2One were unavailable for comment and neither company would confirm what documentation had been taken by officials.

But Orange's Andrew Bramley, head of international roaming, denied the company is in any way involved in price fixing.

"There is no question of any Orange involvement in collusion over price fixing," he said in a press statement. "We have consistently provided the most transparent international call charges."

If the swoop uncovers evidence of price fixing between operators then those companies will incur serious financial penalties.