The tension over Russia has highlighted the growing role Gazprom plays in Britain. The state-owned Russian energy giant is the fourth biggest provider of gas to UK businesses and supplies a roster of blue-chip organisations including the National Health Service, Oxford University and Chelsea football club.

It has also made an office near Regent's Park in London its global headquarters for energy trading, with up to 600 staff employed in the capital and more joining every day.

A UK-registered subsidiary, Gazprom Marketing and Trading (GM&T), produced a net income of £374m in 2012, and paid dividends to its owner of over £100m. In the same year it handed over little more than £20m in UK corporation tax, according to the last annual accounts filed at Companies House.

GM&T's Gazprom Energy arm, based in Manchester, provides 10% of gas used by businesses and boasts a customer base of 11,000.

Gazprom has a long connection with Centrica. The Russian giant considered a £10bn takeover of Centrica in 2006 but backed off amid a political storm in Westminster about the wisdom of selling off the country's biggest domestic energy supplier to Russia.

The gas group had just a few months earlier cut off gas to the Ukraine in what Vladimir Putin claimed was a row over non-payment but was interpreted elsewhere as an attempt to stop Kiev building closer links with the west.

Gazprom similarly turned off the taps in 2009 and again earlier this month over the same issue, but relations between the Kremlin and both Washington and Brussels have really deteriorated since pro-Russian rebels took control of eastern Ukraine.

The annual accounts of GM&T make clear that although it is based in the UK its strategic direction is set in Moscow. "The Group (GM&T) continues to position itself as a crucial interface for the wider Gazprom group. It (GM&T) remains closely aligned with the strategic goals of the Gazprom group, which in turn fully supports the Group (GM&T) in its own ambitions," it says.

A spokesman for Gazprom said the trading arm had been established at Triton Street because the UK had a large pool of experienced people, a useful timezone for trading in Europe, America and Asia plus good airports for international travel.

He said the relatively low tax figure of £20m reflected the fact that much of the profit was earned abroad, often in places like Singapore. He added: "The HMRC (Her Majesty's Revenue and Customs) are happy with this arrangement."

Gazprom was not able to say exactly how much gas comes from Russia to the UK but some estimates have put it at 8bn cubic metres – which would make it more than a 10th of the national consumption. Greenpeace, which monitors Russian energy companies largely because of their activities in the Arctic, believes the figure could be as high as 12bn cubic metres.

The Gazprom spokesman said he didn't recognise either figure but added it was possible these numbers reflected the total amount of gas formally traded through GM&T in London.

Gazprom's retail operations in the UK began in 2006 when the Russian giant acquired a small energy firm based in Cheshire, in the north-west of England, called Pennine Natural Gas.

At the time the gas distribution business employed just 12 people and supplied a handful of clients. But it was quickely re-branded and has since become a major player in the UK's commercial gas market, operating from impressive steel and glass offices in the commercial heart of Manchester, employing around 250 staff and increasing the volume of its gas sales in the UK by 500%.

Gazprom's initial foray into the UK market did not go entirely unnoticed. As far back as 2007 Tory MPs were expressing concern about its stated ambition to become a major supplier of energy to the NHS. One member of the Public Accounts Committee, Richard Bacon, asked at the time: "When you have sick patients … can you really trust Vladimir Putin to be their major supplier?"

But fast forward seven years and it seems those warnings have not been heeded. As David Cameron called for tougher sanctions against Putin's administration last week, Gazprom Energy was quietly supplying gas to a range of high-profile customers – including a number of hospital trusts.

The company declined to divulge details but the NHS confirmed Gazprom Energy supplies several trusts in north-west England in contracts worth £12m.

But its NHS operations are just one element of Gazprom Energy's spectacular growth. Its business customers across the UK range from local authorities to cinema chains, universities to high street shops and schools.

Surveying this growing empire, the company's new global head of retail, Lars Clausen, told its quarterly magazine Energise his aim was to turn Gazprom Energy into "the pan-European leader" in its field.

"There are great opportunities; we can learn from what we've done well in the UK and bring that to Europe."

One of the things competitors say the company has done well in the UK is use its financial muscle to undercut their rivals on price. But a spokesman said its success was based on "offering sophisticated and bespoke energy solutions to corporate clients" rather than simply cut-price gas.

He added: "Gazprom Energy offers its clients flexibility, tailored to their specific business needs. It's not about [the] lowest rate and never has been – it's about designing an energy plan that meets the needs of the client at a good value for money."

The Greenpeace UK energy campaigner Louise Hutchins said it was time to end a system where Cameron talked tough about slapping sanctions on Russia while presiding over an energy system that ploughs millions into the Kremlin's coffers.

"Every time ministers have scrapped funds for domestic clean technologies and failed to cut energy waste, they've made Putin's oligarchs a bit richer and Britain's energy security a bit weaker.

"This is the price we pay for our addiction to fossil fuels, along with climate change, air pollution, and volatile energy prices. If ministers are serious about bulking up our energy security then the cheapest, easiest, fastest way to achieve this is cutting waste and backing clean, home-grown, high-tech power sources."