Compared with the car bomb which killed six people and injured 93 others in 1983, yesterday's attack was minor and none of the victims was seriously hurt.
But the bomb, placed in a litter bin outside the Knightsbridge store, served notice that the terrorists plan to continue their attacks against economic targets in England.
The device, thought to consist of no more than 1lb of explosive, went off in a litter bin in Brompton Road outside the entrance to Harrods' jewellery department. It smashed windows and cracked doors, but caused no damage inside.
Two people were taken to hospital suffering from ear damage and cuts from flying glass, but were discharged after treatment. Two others were treated for minor injuries at the scene.
The terrorists followed their familiar tactic of giving misleading warnings. Two calls using code words were made to Harrods Bank and the Samaritans, each claiming that two bombs had been planted. The call to the bank at 9.14am said that there was one bomb inside the store and another outside due to go off in 30 minutes. The second shortly afterwards also claimed there were two devices but gave less detail.
There were no customers inside Harrods because the store now opens at 10am. But 3,000 employees were inside when the bomb went off at 9.40am.
By this time the store had been searched and declared clear but the staff were not evacuated in case they walked into an explosion. The previous Harrods bomb was hidden in a car and caused almost 100 casualties in the street outside.
In spite of this, some passers-by were reluctant to heed the police. David Edwardes, of Knightsbridge said: 'It was just unbelievable. They were just walking through the plastic barrier tape.'
Harrods reopened shortly before 2pm and will be open as normal today. Michael Cole, spokesman for the store, said: 'If there is any comfort to be gained from this, it is that our procedures worked very well.'
The litter bins, one of which provided a hiding place for the bomb, were replaced by Kensington and Chelsea council only 10 days ago after having been removed over Christmas and New Year.
The council said: 'Following consultations with the police we removed them for security reasons on 18 December and replaced them on 18 January. I do not know whether they will now be taken away permanently.'
Mr Cole said Harrods had expressed reservations about the bins being replaced. It was the first IRA bomb to explode in England this year, although several incendiary devices have gone off in the capital. One person was killed and almost 90 injured in a pre-Christmas terrorist campaign.
Martin McNamee, 25, a plumber, was killed in a loyalist bomb attack intended for the owner of a house where he was working. The outlawed Protestant Ulster Volunteer Force admitted it rigged the device at a house under construction near Cookstown, Co Tyrone. Mr McNamee was the first Catholic to be killed by a loyalist bomb in Northern Ireland for almost 10 years. A second man was slightly injured in the blast.