For millions of commuters travelling to work in London yesterday, the journey had a weary familiarity as railway stations were shut by bomb scares and roads closed by police checkpoints.
Security measures returned to pre-ceasefire levels with police carrying guns back on the streets of the capital and it was announced that for the first time armed officers are guarding the Channel tunnel terminal at Folkestone in Kent.
In London, there were few major travel hold-ups, but the frustrating closures and niggling route changes that were a part of commuting life before the IRA ceasefire began in August 1994 were back with a vengeance.
"I think this may be what Londoners and commuters are going to have to get used to again," said a spokeswoman for London Underground, which had half a dozen stations closed by suspect packages during the morning rush hour.
"What we are hoping is that people will return to the levels of watchfulness and security awareness that we had grown used to prior to the 18-month ceasefire."
Mainline stations including Euston, Waterloo and Liverpool Street were closed for an average of about 15 minutes. Elsewhere in the network tannoy announcements of closures were received with an air of resignation by travellers.
British Transport Police searched King's Cross, St Pancras, Euston and Paddington railway stations after a bomb warning, but they did not close the stations because no recognised code word was received and disruption was kept to a minimum.
The so-called "ring of steel" which was introduced around the City of London in July 1993 after the Bishopsgate bombing was brought back to its pre-ceasefire operational level.
A year ago the number of police guarding the eight checkpoints into the financial heart of the capital was scaled down and since then some have only been manned on an irregular basis.
However, the 900-strong City of London force retained the 100 extra officers it had recruited to cope with the increased workload.
They are backed up by 27 recently installed checkpoint entry cameras which photograph the numberplate of every vehicle and the face of every driver who enters the City of London.
Another 13 cameras take pictures of vehicles leaving the City and there are 48 traffic cameras elsewhere.
In another move back to the pre-ceasefire atmosphere, armed officers have been back on the streets of the capital , mounting roadblocks and stopping and searching vehicles.
Sir Paul Condon, the Commissioner of the Metropolitan Police, said in an appeal to Londoners yesterday: "Please be tolerant and understanding of the divisional arms control you may see on the streets and be co-operative if we ask to search you or your vehicle."
"My appeal to you is to go back to the level of vigilance all of you took for granted before the ceasefire for your own sake and to help the police."
Kent Police said yesterday that armed patrols carrying semi-automatic weapons were introduced at the terminal at the entrance to the Channel tunnel within hours of Friday's explosion.
However, these armed patrols would not extend to trains travelling to France.
Superintendent Cliff Grieve, the officer in charge of Channel tunnel policing, said: "We do have a fairly strong security regime here but we are not impregnable.
"What we want to do here is give a message of reassurance to Eurotunnel's customers that this is a fairly safe environment in which to travel.
"But it is also a message to the terrorists that we are here and we have an armed presence here as well.
"There is no specific threat to the Channel tunnel and these measures are purely designed on the basis that it is a high profile target."
Police in Birmingham warned the public to be extra vigilant amid fears that last weekend's attack is the beginning of a mainland terrorist campaign.
West Midlands Police stressed that although there is no specific threat to the area they were raising their own security levels and urging the public to do likewise - in line with other forces covering major cities.
The Assistant Chief Constable, Bob Packham said: "We want the people of the West Midlands to carry on with their lives as usual and our officers will continue to work hard to minimise the risk of further attacks.
"However, we must be conscious that terrorists could strike at any time and any place and there is a need to raise people's awareness about increasing security and vigilance."
The Assistant chief constable added that the policing operation at Birmingham's International Airport, where an armed presence remained throughout the ceasefire, would continue at a high level.Reuse content