LONDON - FOUR extremists jailed for plotting a wave of suicide bomb attacks in London on Wednesday lost their bid to challenge their hefty convictions.

Three Court of Appeal judges dismissed their applications for leave to appeal against their sentences for conspiracy to murder, which condemned them to serve at least 40 years behind bars.

On July 21, 2005, the four tried to detonate rucksacks laden with explosives on three London Underground trains and a bus, but the bombs failed to explode.

The planned attack came exactly two weeks after a near-identical plot succeeded, killing the four Islamist bombers and 52 others in the deadliest such attack on British soil.

Muktar Said Ibrahim, Ramzi Mohammed, Yassin Omar and Hussain Osman were jailed for life in July last year after being convicted.

One of the three appeal judges, Sir Igor Judge, said: 'These were merciless and extreme crimes. As they were rightly meant to be, the sentences were severe and extreme.

'Beyond doubt, however, they were utterly justified.' -- AFP