UK telecoms watchdog Ofcom has opened an investigation into BT's wholesale pricing of voice calls, prompted by complaints from telcos Thus and Gamma Telecom.

Both companies accuse BT of anti-competitive practices in contravention of the Competition Act 1998 and Article 82 of the European Treaty.

Specifically, they allege that BT has been pricing wholesale end-to-end calls to resellers at below cost since April 2005, with the deliberate aim of driving down the margins for competitors – like Thus and Gamma – and consequently putting them out of business.

Ofcom's investigation will decide whether BT has abused its dominant position in the wholesale voice connections market.

While Thus is the telco spin-off of Scottish Power, formed in 1999, Gamma, founded five years ago, focuses on selling telecom services to small businesses.

The complaint has been supported by Cable & Wireless.