Oil worker told the BBC's Panorama programme that both BP and Transocean, who owned the rig, were informed of the leak

An oil worker who survived the BP Deepwater Horizon explosion has claimed that the oil rig's safety equipment was leaking several weeks before it exploded, triggering the huge spill in the Gulf of Mexico.

Tyrone Benton says that he spotted a leak on the rig's Blowout Preventer (BOP), the device that is meant to shut the well down if there is an accident. He told the BBC's Panorama programme that both BP and Transocean, who owned the rig, were informed of the leak, and the faulty part – a control pod – was switched off rather than being repaired.

"We saw a leak on the pod [and] we informed the company," Benton told the programme, which will be broadcast at 8.30pm tonight. "They have a control room where they could turn off that pod and turn on the other one, so that they don't have to stop production."

Benton added that he was unsure whether the leaking control pod had been turned back on again before a huge gas explosion ripped through the rig on 20 April, killing 11 workers.

The failure of the BOP was one key factor that led to the ongoing environmental disaster. The BOP is designed to clamp the well tightly shut, using cutting equipment to slice through the casing, but on 20 April it did not engage.

After the explosion, BP sent robot submarines down to the seabed to try to trigger the BOP, but failed. The company has already admitted to a Congressional committee that the robots discovered a leak in the BOP's hydraulic systems, which meant they could not generate enough force for its giant shears to cut through the pipe.

Last week, BP chief executive Tony Hayward repeatedly cited the BOP as a major cause of the disaster, saying it was "not as failsafe" as BP had been told.

Benton's revelations will pile even more pressure on BP, at a time when its minority party in the leaking well is refusing to pay its share of the costs. Anadarko Petroleum Corporation argues that BP was "grossly negligent" or guilty of "willful misconduct" in the way it drilled the Macondo prospect, which some workers described as a "nightmare well". Last week the Congressional committee accused BP of taking "risky" decisions to save time and money.

And in another development, BP has been accused of lying after internal documents showed that it has estimated that the leak could reach 100,000 barrels a day, much higher than its public forecasts.

$2bn and rising

The cost of the clean-up operation has now broken through the $2bn (£1.3bn) mark, BP told the City this morning. That is just a fraction of the total bill, though, with BP already committed to putting $20bn into an escrow account to cover compensation claims. That will not cap its liabilities, though, and there are suggestions that BP is now looking to raise $50bn.

The company has said it will sell off some of its assets. This has raised concerns in several countries, including Russia, where the TNK-BP joint venture generates around a quarter of BP's global production.

Hayward is to fly to Russia to assure the Kremlin that BP can survive the oil spill disaster, the Financial Times reported today.

BP's chief executive took the decision to meet Russian president Dmitry Medvedev in the next few weeks following a weekend board meeting, and after Medvedev warned that the catastrophe could lead to BP's "annihilation".

BP continues to insist that it will clean up the spill and pay "all legitimate claims", and rejected Anadarko's claims.

"These allegations will neither distract the company's focus on stopping the leak nor alter our commitment to restore the Gulf coast," said Hayward. "Other parties besides BP may be responsible for costs and liabilities arising from the oil spill, and we expect those parties to live up to their obligations."

Shares in BP fell by more than 3% this morning to 345p, making it the biggest faller on the FTSE 100. Swiss bank UBS warned shareholders that it did not expect the company to resume paying dividends until 2012. Last week it agreed to cancel payments for the rest of this year, but UBS believes that the cost of the Deepwater spill means a longer suspension is inevitable.

City sources believe that BP may have to sell its operations in the North Sea as part of its drive to cut spending and raise funds.