"Downing Street has discreetly let it be known in the City that it would oppose any takeover of BP," the Financial Times reported on Sunday.

The prime minister's office has signaled it would make life difficult for any bidder, although no bid has been mooted yet, the newspaper said ("UK ministers make Gallic gesture to keep the British in BP", April 26).

The company formerly known as British Petroleum was rebranded as the more neutral BP at the turn of the millennium after absorbing U.S. oil firms Amoco and Arco.

But the company's identity remains complicated, at once BP and British Petroleum, part of Britain's establishment but also a footloose international oil major with operations around the world.

Much more than Royal Dutch Shell, with its historical link to the Netherlands, BP is Britain's national oil company and bears with it the country's hopes for a major post-imperial role.

BP continues to have a close relationship with Britain's establishment - reaching beyond government ministers, who come and go, right into the core of the permanent Whitehall bureaucracy as well as the media and London's financial managers.

When the company was pilloried by U.S. politicians as a careless foreign operator in the wake of the Deepwater Horizon oil spill in the Gulf of Mexico, the company took pains to play down its Britishness and emphasize it was a good American corporate citizen.

But at home, the company mounted an effective public relations campaign to enlist support from ministers and the British media to push back against what it presented as a strategic threat to the United Kingdom. BP wrapped itself in the national flag at home, while presenting itself abroad as a post-national corporation of the world.

ANGLO-PERSIAN

From the very beginning, British Petroleum, formerly the Anglo-Iranian Oil Company and before that the Anglo-Persian Oil Company, has had close links to the state.

The company owes its existence to an unusual government investment of just over 2 million pounds into the firm in May 1914, masterminded by Winston Churchill, then serving as Britain's minister for naval affairs.

Churchill was determined to ensure a reliable source of oil for the Royal Navy from within Britain's empire to avoid a dangerous dependence on the United States, Russia or the Dutch East Indies ("The Royal Navy's Fuel Supplies 1898-1939", 2003).

The advantages of liquid petroleum over solid coal as fuel for warships were "inestimable", Churchill wrote later ("The World Crisis", 1938).

"But oil was not found in appreciable quantities in our island. If we required it, we must carry it by sea in peace and war from distant countries ... An unbroken series of consequences conducted us to the Anglo-Persian Oil Convention," Churchill explained.

Persia was formally independent, but the country, especially its southern half, where the oilfields lay, was firmly within Britain's sphere of influence, while the north lay in Russia's.

Britain's investment gave the government a voting stake of just over 50 percent in the company and provided capital at a critical point when the firm was seeking to develop its new fields in southwest Persia.

In exchange, the Royal Navy received a guaranteed supply of oil below market prices and Britain's government received hundreds of millions of pounds in dividends and tax revenues, far more than Iran ever received ("Blood and Oil: A Prince's Memoir of Iran from the Shah to the Ayatollah", 2005).

In 1951, when Iran nationalized the assets of the Anglo-Iranian Oil Company, Whitehall helped organize a worldwide boycott of Iran's oil sales (the forerunner of the current sanctions regime) in a bid to reverse the nationalization or at least win substantial compensation.

Following nationalization, Whitehall, encouraged by Churchill, serving in his last term as prime minister, plotted to overthrow Iran's democratically elected government, in a plan codenamed Operation Boot.

In the end, it was the United States that took over the plan, and fomented a coup in 1953, codenamed Operation Ajax.

Prime Minister Mohammad Mossadegh was overthrown and Shah Mohammad Reza Pahlavi was installed as an autocrat, until he too was overthrown in 1979 by Ayatollah Ruhollah Khomeini.

"Even in Persia, they were never quite convinced that I had not come straight from Whitehall," Lord Strathalmond, chairman of Anglo-Iranian between 1941 and 1956, recalled later ("Adventure in Oil: The Story of British Petroleum", 1959).

BP AND WHITEHALL

Nationalization was traumatic but the company, renamed British Petroleum, successfully reinvented itself by developing new fields in Kuwait, Alaska, the North Sea and around the world.

The British government's remaining stake in British Petroleum was eventually sold in 1987 as part of the privatization program of the government of Prime Minister Margaret Thatcher.

But the company, renamed BP after the mergers of the late 1990s, has retained close links to the very apex of the British government under both Conservative and Labour-led administrations.

For example, Anji Hunter, one of the most senior aides to Labour Prime Minister Tony Blair as head of government relations in the late 1990s, went on to become director of communications for BP in 2002.

She also married one of the top political journalists at broadcaster Sky News, and now works as a senior adviser to public relations company Edelman.

Nick Butler, who worked for many years at BP, rose to become group vice-president for strategy and policy between 2002 and 2007, before becoming a senior policy adviser in the prime minister's policy unit at Downing Street in 2009-2010 under Labour Prime Minister Gordon Brown. Butler now blogs for the Financial Times.

Ben Moxham, who served as director for policy and regulatory affairs at BP and then vice-president at Riverstone Holdings, the investment firm where former BP chief John Browne is a partner, went on to be the senior adviser on energy and the environment to Conservative Prime Minister David Cameron and Liberal Democrat Deputy Prime Minister Nick Clegg between 2011 and 2013.

Browne himself, ennobled in 2001 as a member of the House of Lords, the unelected upper chamber of Britain's parliament, has undertaken a number of high-profile government assignments since stepping down as head of BP in 2007.

Close relations between Whitehall and business, including the exchange of personnel between the civil service and major corporations, are normal in Britain, but no other company has had such close links to the very top of government.

BP is not just another large company listed on the London Stock Exchange that could be taken over by a foreign corporation at the right price. It is part of the establishment.

BP's history is the story of the last days of the British Empire. And with its reinvention after the Iranian crisis in the 1950s, BP has become the flag-bearer for Britain's hopes of remaining a global player in the oil industry, albeit with a much diminished role.

For BP to fall into foreign ownership, and cease to be British Petroleum in fact as well as name, would intensify the establishment's existential angst about Britain's future role in the world and is simply unthinkable.