The alert shook a community still grieving over Saturday's litter bin bombings in which three-year-old Johnathan Ball died, and fuelled fears that Warrington had been targeted by IRA bombers for the third time in less than a month.
The Prime Minister, speaking of the weekend attack, told Parliament yesterday: 'If there were a shred of humanity in the IRA, they would hand those killers over for justice without any delay.' If not they would be 'hounded for the rest of their days', he said.
Police said the device had been planted at the same time as the first bomb attack on the site, which happened on 26 February, but had burnt itself out behind lagging without doing any apparent harm.
Three explosions ripped through the site, wrecking one of the site's three gas holders and badly damaging another. One unexploded incendiary device was found shortly afterwards. The device found yesterday was planted next to the third holder, the only one still in operation.
Superintendent David Williams said: 'We are obviously making a further check but this is debris from the first incident.' He said that the cassette-sized incendiary would have been missed by sniffer dogs because it was made from sugar.
The incendiaries would have been planted together with the three high explosive devices to ignite leaking gas and cause maximum impact.
More than 200 people were evacuated from their homes. Roads were closed off in the Winwick Road area near the town centre and services on the main west coast railway line were stopped for about two hours. The alert came at a time when the people of Warrington were still coming to grips with the aftermath of Saturday.
Police have had a massive response from people who were in the Golden Square shopping centre when the bombs went off. The information they have given to the police is being checked against a special video playing facility the force has set up to study video recordings made by automatic security cameras in nearby shops.
On a visit to Warrington yesterday, the Archbishop of Canterbury, Dr George Carey, paid his respects at the makeshift shrine, marked by floral tributes, near where Johnathan Ball was killed. He asked God that 'out of this terrible tragedy you will bring to justice those who caused this terrible inhuman act'.
Twelve people injured in the bombings were still being treated at Warrington General hospital yesterday.
The two most seriously injured, Bronwen Vickers, 33, who had a leg amputated, and Stephen Clague, 21, who suffered arm, elbow and hip injuries, were both said to be 'stable'.
Mrs Vickers' husband Paul, 37, is among the others injured. They were all in a 'satisfactory' condition.