A 500lb German bomb was found in Portsmouth Harbour during dredging work ahead of the arrival of HMS Queen Elizabeth.

The Second World War device was found at 5am this morning by a barge dredging the harbour – part of a raft of infrastructure upgrades taking place in readiness for the arrival of the Royal Navy’s new 65,000-tonne aircraft carrier.

As a precaution a 500-metre cordon is in place around the barge. Royal Navy bomb disposal experts then moved the device further into the harbour to allow Portsmouth’s continental ferry port to temporarily re-open.

When tidal conditions permitted, the bomb was towed out to open waters 1.5 miles east of the Isle of Wight, where a controlled explosion took place at 4pm. Shipping movements were restricted while the device was towed out through the harbour entrance.

Commander Del McKnight, the Commanding Officer of the Royal Navy’s Fleet Diving Squadron, said: ‘Everything went smoothly and we were pleased to be able to get the operation completed in daylight today. Despite being old, these devices still pose a very serious threat when they are moved.

‘Last year we had more than 450 call-outs around the UK so this is really business as usual for us. We’ve had more call-outs to Portsmouth than we would usually see, because of the extent of the dredging works being done to make way for HMS Queen Elizabeth, but we have teams on standby at 10 minutes notice around the UK ready to deal with these things.’

The bomb found in Portsmouth Harbour

The Second Sea Lord and Deputy Chief of Naval Staff  Vice Admiral Jonathan Woodcock shared photographs of the device on Twitter and said: ‘This is the bomb found in Portsmouth Harbour today. Our cool as a cucumber Royal Navy bomb disposal team sorted it and the harbour’s open.’

Mark Rodaway, strategic gold commander for the UK Coastguard said: ‘This ordnance appears to have been left over from WWII and has remained for many years undisturbed on the seabed.

‘We are treating it as potentially unstable and in order to keep to the public safe, we worked with Hampshire Police and the Queen’s Harbour Master to evacuate a large section of the Portsmouth harbour area – including Gunwharf Quays, Old Portsmouth and The Hot Walls.

‘These cordons have now been lifted.’

Millions of pounds have been spent on works to prepare Portsmouth Naval Base to accommodate the Royal Navy’s two new aircraft carriers – HMS Queen Elizabeth and HMS Prince of Wales.

Dredging operations are under way to deepen the main channel used by shipping in Portsmouth by one metre. New power facilities are also being built, navigational aids installed and jetties upgraded to take the carriers alongside.