The Government would be prepared to approve a takeover of BP by its larger rival Shell rather than allow it to fall into overseas hands. 

The informal guidance in Whitehall was provided before last week's reports that Shell was in early-stage talks about a possible takeover of its weaker competitor.

Shell issued a statement to the stock exchange saying that no such talks were taking place. 

Under Britain's strict takeover rules, it is not permitted to make an offer for six months. It would require BP to invite Shell into the process should there be a bid from other sources.

City investment bankers have been floating the idea of a Shell-BP deal to create a London-based European oil champion on the scale of the American behemoths for some months.

Such a transaction would inevitably require scrutiny by anti-trust authorities on both sides of the Atlantic.

Shell chief executive Wael Sawan publicly has made it clear that his target is to keep returning funds to shareholders through dividends and buybacks, which have been running at £3 billion a quarter.

A takeover of BP is seen at Anglo-Dutch Shell headquarters as a distraction from its core mission.

Nevertheless, the company felt it necessary to take informal soundings with Ministers and officials, should the opportunity to become involved with BP arise.

Shell's last major UK takeover came when it bought BG Group, once the exploration arm of British Gas, for £46 billion a decade ago.

Shell, with a stock market value of £150 billion, has accelerated away from BP in recent years. With a valuation of less than half that, BP would be easy pickings for most of the big oil firms.

Investor interest in big oil has increased since Donald Trump returned to the White House with his 'drill, baby, drill' mantra.

The open hostility of Keir Starmer's Government to fossil fuels has also softened in recent weeks. The 12-day war between Israel and Iran has been a sharp reminder of how important oil and gas is to the UK's energy and national security.

BP's low valuation of £58.8 billion makes it an attractive takeover proposition for its rivals.

It has been beset by problems in the boardroom, in Russia and in the newly named Gulf of America. It carries net debt of £20 billion on its balance sheet.

BP is seeking to refocus on oil and gas exploration and production after flirting with becoming a carbon-zero energy group under Bernard Looney, who left under a cloud in 2023.

Current chief executive Murray Auchincloss has set a challenging target to reduce net debt to £14 billion by 2027. 

It is also under pressure from activist investor Elliott Capital Management to improve early returns even if it means cutting back on capital investment.

However, it is not clear that the big American oil companies would be interested in buying BP.

Exxon Mobil is very focused on the Americas, having struck black gold in the Guyana basin. It is also deeply involved in drilling, fracking and extraction of natural gas in the Permian Basin in Texas and New Mexico with its $64 billion (£47 billion) takeover of Pioneer Natural Resources.

Rival Chevron also has been doubling down on domestic development and is pursuing a $50 billion takeover of Hess Corporation, although this has been bogged down in an arbitration process.

As the former Anglo-Persian oil company founded in 1909, BP has a long history of global exploration and good relations with the British Government. It has lost none of its adventurous nature and has been developing new production and markets in Azerbaijan, India and Indonesia and is a big investor in Iraqi production.

The Government will fear for the fate of such a vital flag-flier for Britain at home and abroad, and for the risk to jobs, exports and oil trading should it fall into overseas hands. A loss of its London stock exchange quotation would be a devastating blow to the UK.

Some City advisers have been alerted that their services will be needed should, for any reason, the current six-month cooling-off period on a Shell-BP transaction be interrupted.