It was an indiscriminate attack Bomb Squad Chief Robert Huntley

"It is the sort of target the IRA would pick," he continued, although the incident happened without the coded warning typical of the organisation.

Constable of the Tower Major General WDM Raeburn has revealed that he received a message last Sunday that "the Tower is going up".

But a thorough search found nothing at the time and Master of Armouries Richard Dufty claims that this afternoon's bomb would have been noticed by his staff if it had been there for any length of time.

All that remains of the device is an electro-magnetic timer, found near the cannon where detectives think the bomb was left.

Police are checking camera films used by visitors for any further clues.

They are particularly interested in the pictures of photo-journalist Jean Halgen who thinks she may have a shot of a man she saw running away from the scene aged 30-33 of medium height with brown hair and wearing a brown jacket.

The dead woman has been named as Dorothy Household, 47, a librarian in Lewisham who was visiting with a friend and two children.

This is the second bomb in London today. At 0430 BST there was an explosion at government buildings in Balham, South London.

Nobody was injured in this morning's blast but there was substantial damage to surrounding buildings.

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