The bombs were in panniers on bicycles left outside their targets in Bognor Regis and Brighton, 15 miles apart on the south coast.
Detectives investigating the attacks, involving bombs 'big enough to maim and kill', believe that the bicycles may have been rented because of the codes painted on the frames and locks.
Yesterday, police carried out a finger-tip search of the debris left by the explosion in Bognor just before 6pm on Saturday, which wrecked 15 shopfronts.
The second device, left on the forecourt of the Palace Pier at Brighton, was made safe by a controlled explosion after it had been found during a search.
Both attacks were accompanied by telephoned warnings, but the information about the location was so general that police said they were unable to act effectively.
The bombs served to emphasise the gulf that still has to be bridged between the IRA's campaign of violence and the hopes for peace which, after 25 years, are higher than ever as Republican terrorists appear on the brink of calling at least a temporary ceasefire.
The bomb at Bognor exploded at 5.57pm outside Woolworth's in the pedestrian precinct in the London Road area.
Marcus Halsey, whose shop was wrecked, said yesterday that a chat with a colleague had probably saved his life.
'There was just a bang, the glass all blew in and I was lifted off my feet and then back on the floor,' said Mr Halsey, nursing bruised ribs. But he would normally have been upstairs, where the windows were not toughened, at the time the bomb went off.
'If I had been, I would not be here today,' he said. 'The upstairs is just totally wrecked. The glass has just blown right across the room and is embedded in the walls.'
Among the debris police found a Townsend Oregon mountain bike that had the numbers 20-2 written in white correcting fluid on the part of the frame which leads from the handlebars to the front forks. A D-lock, used to secure the cycle, had the number 26 written in the same type of fluid.
After the Bognor blast and a second vague warning, police closed off the Palace Pier in Brighton and discovered the second device strapped to a French-made Gitane Bullet, secured to railings using a D- lock on which the number 16 was written in correcting fluid.
The Assistant Chief Constable of Sussex, Richard Childs, appealed for anyone who had information about the bikes to contact police, emphasising that people near the pier entrance at Brighton may have taken photographs or shot videos which could hold a vital clue.
Mr Childs also warned that it was imperative for everybody to be vigilant and report anything or anyone suspicious. 'It is now obvious we are in the middle of an IRA mainland campaign,' he said.
As the piers at Brighton and Bognor remained sealed off while searches continued, police began house-to-house inquiries in Bognor and the lengthy task of examining security videos from shops.
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