The arrests, which are considered a significant break-through, followed raids in London and South Armagh yesterday morning. Further arrests are expected soon.
But in an ominous development yesterday an Irish plain-clothes detective was shot dead and another critically wounded in what gardai believe was an IRA fund-raising robbery in the Limerick village of Adare. The IRA denied any involvement in the incident - its members have long been under orders not to fire at Irish security forces.
The arrests of the five men in connection with the blast at South Quay in east London on 9 February are understood to have been a result of information obtained from surveillance cameras and from witnesses.
The men are being questioned about the lorry bomb as well as a number of other terrorist attacks. This is expected to include the two Semtex bombs that were planted at the south side of Hammersmith Bridge in west London in April.
Four of the men were detained in South Armagh as Scotland Yard anti-terrorist officers, supported by the RUC and the Army, searched farm outhouses near the village of Forkhill. The four were flown to London for questioning.
The fifth man was arrested in Barking, east London, under the Prevention of Terrorism Act.
Irish police last night named the dead policeman as Gerry McCabe 52, from Ballylongford, County Kerry, a father of five. Ben O'Sullivan, 52, from Cork, who was also shot was taken to hospital in a critical condition with shoulder and facial injuries.
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