Washington is to investigate whether BP has been sufficiently punished for allegedly manipulating the American propane price.

This week, it emerged that BP had agreed to pay $303 million (£148 million) to settle civil charges that it deliberately sought to fix the price of propane in 2004 by cornering the market.

However, the House Energy and Commerce Committee on Capitol Hill said yesterday that it had launched an inquiry into whether the settlement represented a big enough deterrent.

BP is the biggest supplier of propane in the United States, where it is used by millions of Americans to heat their homes and cook food, particularly in rural or poor communities where there is no access to an ordinary gas supply.

John Dingell, the congressional committee’s chairman, said in a statement: “We are specifically interested in determining whether the penalties levied are sufficient deterrents to improper behavior . . . In light of this settlement, the Energy and Commerce Committee will investigate whether government agencies acted appropriately during pricing negotiations with BP.”

The committee is no stranger to BP, having investigated the company’s refinery blast in Texas two years ago and a burst pipeline in Alaska.

It is expected that the US Justice Department and the Commodity Futures Trading Commission (CFTC) will announce the settlement deal with BP today. In a 42-page complaint filed in a US district court in Illinois in June 2006, the CFTC alleged that “with the knowledge, advice and consent of senior management, BP employees developed and executed a speculative trading strategy in which BP cornered the February 2004 . . . physical propane market.”

It is thought that while BP has settled the civil charges made against it, it has also agreed to make certain operational changes to defer any criminal proceedings, which include being overseen by a government-appointed regulatory monitor for between three and five years.

The office for the committee failed to return calls yesterday and BP has refused to comment.

The decision to settle the charges comes as part of a fresh approach by Tony Hayward, BP’s new chief executive, to draw to a close a miserable few years.

BP is also under investigation by American regulators for abusing its size to manipulate the price of crude oil.

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