Scotland Yard decided to keep open one section of the M25, which was named in an IRA coded telephone call, although officials denied they were taking a tougher approach to terrorist warnings.
Kent, Hertfordshire, and Hampshire police also reacted quickly to a series of coded bomb threats, by closing down stretches of motorway, but re-opening them within hours.
The speed with which the forces dealt with the emergency reflect their growing expertise with the tactics, but may also indicate a more hard- line response to efforts to cause travel and economic chaos.
The latest attempt by the terrorist organisation to force its way on to the election agenda comes less than 48 hours before polling starts and amid an unprecedented crackdown by the police and security forces.
Despite the prompt response to the threats tens of thousands of travellers had their journeys disrupted yesterday morning.
The alerts closed sections on the M1, M3 and M25, leading to tailbacks of up to 25 miles, and there were also evacuations at Heathrow, Gatwick and Southampton airports.
One of the warnings covered junctions 14 to 16 of the M25 either side of Heathrow airport, but following a search of the area anti-terrorist officers at Scotland Yard decided not to close the motorway. Two other sections of London's orbital motorway - in Kent and Hertfordshire - were closed.
A spokeswoman for the Metropolitan Police said yesterday that the decision to keep the road open followed careful assessment of the threat to the public. "We are continuing our current policy, it would be wrong to presume that we are taking a tougher stance than usual - each case it looked at on its own merits," she said. Some terrorism experts and newspapers had suggested recently that the police were too willing to close roads.
In Kent sections of the M25 and M20 were closed at 6.50am but were reopened by 8.30am. A spokesman said: "The more you do something, the more proficient you become, although it is difficult to compare different security alerts."
Among the worst delays was the closure of a seven-mile stretch of the M1 in Hertfordshire between 7.15am and 11.45am and sections of the M3 and M27 in Hampshire were closed shortly before 8am and reopened just after 10am.
Heathrow's Terminal Two was partially evacuated for 22 minutes and Gatwick's north and south terminals were both partially evacuated for nearly two hours. Gloucestershire police later closed the M5 over a 20-mile section following a "suspicious incident".
Jack Straw, Labour's home affairs spokesman, cancelled a flight to Plymouth because of the alert at Gatwick. He said: "From the reaction of people at Gatwick, I can tell the IRA and Sinn Fein that their activities are stupid and counter-productive and simply stiffen the resolve of the British people not to give in to terrorism."
Loyalist inmates at the Maze prison outside Belfast yesterday staged rooftop protests in the wake of a proposed security clampdown arising from the recent discovery of an IRA escape tunnel at the jail.
Prisoners affiliated to the Ulster Defence Association set fire to two observation posts and broke out on to the rooftops of two of the Maze's "H-blocks" to display banners. Staff were withdrawn from the vicinity of the protests for their own safety.
The disturbances followed the introduction of extra security measures in the wake of the IRA attempt to stage a large-scale break-out. The new measures include more random searches, twice-daily lock-ups and more head- counts.
Ironically, IRA prisoners have accepted the new regulations without demur, and yesterday gave no trouble.
John White, prisons spokesman for the Ulster Democratic Party, warned that unrest could spread outside the jail. He said: "The prisoners are very angry. They feel very strongly about it and are prepared to protest to prevent it happening, and so are the organisations on the outside."
Last night it emerged that Billy Wright, the prominent Portadown loyalist recently jailed for intimidation, had joined in the protest. He is associated with a small but particularly militant breakaway loyalist group.Reuse content