Russian energy giant Gazprom has entered the British commercial gas market, after buying the supply side of the UK's largest privately-owned gas supplier.
The world's biggest gas exporter said it has won the right to buy Pennine Natural Gas outright.
Leeds-based firm Pennine has customers such as Debenhams and William Hill.
The takeover now means some 600 customers will have their gas supplied by a firm called GM&T (Gazprom Marketing & Trading) based in London.
Gas will be transported from Russia via the Interconnector pipeline from continental Europe.
Gazprom is seen as a potential suitor for Centrica, parent of British Gas, after it said it aims to secure a fifth of the British wholesale gas market by 2015.
The Russian firm signed a deal with Denmark's DONG Energy last week to buy one billion cubic metres of gas a year for a period of 20 years.
But Professor Jonathan Stern, director of gas research at the Oxford Institute for Energy Studies, last night downplayed suggestions that state-owned Gazprom was being used to wield political influence.
"I don’t think Gazprom will buy British Gas but it wouldn’t alarm me particularly if it did," he said.
"Our consumers have a choice, they don’t have to stay with anybody they don’t like, if they don’t like being supplied by somebody Gazprom buys they can switch to another supplier."
He said the UK would only be dependent for more than a few per cent of supplies on Gazprom.