An RAF Nimrod flying over southern Afghanistan put out a Mayday call and made an emergency landing at Kandahar air base on Monday after crew found fuel pouring into the bomb bay.

The aircraft was in the middle of refuelling when the crew discovered what several sources described as "a major fuel leak" in the bomb bay. The pilot immediately declared an emergency and broke off refuelling.

It is a repeat of an incident in September last year, when an RAF Nimrod exploded over Kandahar province killing all 14 on board. The board of inquiry into that incident has yet to report but that Nimrod, tail number XV230, had just refuelled in mid-air and the board's initial findings blamed pressure from the air-to-air refuelling system for forcing a serious leak.

The pilot of XV230 reported a fire in his bomb bay and attempted to land at Kandahar. He dropped 20,000 feet in just 90 seconds but at 3,000 feet the starboard wing exploded, followed by the rest of the aircraft.

One leaked e-mail from the pilot of a Nimrod revealed that the aircraft were back flying over Afghanistan within two days and refuelling in mid-air two days after that. "We've not heard a dicky bird, then suddenly the air component commander in the Gulf wants us airborne and tanker- capable again," he said in an e-mail to a former colleague. "So, we had a jet air-to-air refuelling over Kandahar four days after the accident!! Unbelievable. I can't see how that could ever possibly be considered to be good risk management."

It was grounded briefly in February after the discovery of a dent in a fuel pipe but despite the problems the aircraft based in Afghanistan have continued refuelling in mid-air.

The Ministry of Defence said today that nobody on board had been hurt in the latest incident. Air-to-air refuelling had been suspended "as a precautionary measure" but the fleet had not been grounded.

"An engineering investigation into the source of the fuel is under way in accordance with normal practice and appropriate action will be taken as necessary, " an MoD spokesperson said.

Graham Knight, whose son Ben died on board XV230, said that the Nimrods should have been grounded after the explosion. "To allow air-to-air refuelling after just four days was almost reckless. I just find it incredible that they could keep putting crews' lives at risk not knowing what caused the problem."

Jimmy Jones, a former RAF engineer who worked on the Nimrod trials in the late 1960s, said the fleet should have been grounded until the RAF knew what had caused the explosion and the problem was fixed.

Today he renewed his call for the aircraft to be grounded. "It should be grounded until the cause of XV230's accident is determined and corrected. In my opinion it is criminal to continue until that point has been reached."

But the aircraft's capability to feed real-time video surveillance of the battlefield direct to commanders on the ground is seen as so vital that mid-air refuelling has been kept in place.

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