People watching a controlled detonation of a World War Two bomb in Portsmouth were left disappointed – after the explosion was so small that Royal Navy experts didn’t even realise it had happened.

The bomb disposal unit attempted to detonate the 500kg bomb at 0700 this morning, but thought they had been unsuccessful as there had been no plume.

When they returned to blow up the device at 1100, an event attended by media and spectators, they discovered that the bomb had actually exploded during the first attempt – and that a second detonation was no longer necessary.

The Royal Navy will perform a controlled explosion in Portsmouth harbour after a World War Two bomb was found out at sea.

The 500kg German device will be detonated between 1000 and 1100.

The device was located by a barge carrying out dredging works ahead of the arrival of the Navy’s new aircraft carrier – HMS Queen Elizabeth – next spring.

At midnight last night, Royal Navy bomb disposal experts towed the device into open waters 1.5 miles east of the Isle of Wight to prepare for the controlled explosion.

Royal Navy officials say the impact on boat movements in the area will be minimal.

A controlled explosion due to take place in the middle of the Solent has been delayed this morning.

A WW2 bomb was discovered in Portsmouth Harbour yesterday evening, which meant clubbers and shoppers were called to leave Gunwharf Quays and the surrounding areas.

It was found by a system dredging the seabed at around 9.15pm. The device was due to be blown up at 7am but delays mean it will be later this morning.