The chief executive of BP has resigned less than four years into his tenure after admitting that he failed to fully detail relationships with colleagues. Bernard Looney who has spent his entire career with BP, has departed the £88bn company immediately in a surprise move.

The company has informed investors that Looney “did not provide details of all relationships and accepts he was obliged to make more complete disclosure”.

The company said that Looney disclosed “a small number of historical relationships with colleagues prior to becoming CEO” during a review last year, triggered by information from an anonymous source. The Guardian reported.

At that time, no breach of the company’s code of conduct was found. However, BP said its board “sought and was given assurances by Mr Looney regarding disclosure of past personal relationships, as well as his future behaviour”.

Further allegations were recently made and an investigation, involving external legal counsel, is ongoing. BP said: “Mr Looney has informed the company that he now accepts that he was not fully transparent in his previous disclosures.

“The company has strong values and the board expects everyone at the company to behave in accordance with those values. All leaders in particular are expected to act as role models and to exercise good judgment in a way that earns the trust of others.”

Murray Auchincloss, the company’s chief financial officer, will run the business on an interim basis.