Four men jailed for life for their part in attempted suicide bombings in London in July 2005 had their appeal bids turned down on Wednesday after the judge branded their crimes "merciless".

The men, who were sentenced each to spend at least 40 years behind bars for a plot to bomb three underground trains and a bus two weeks after 52 people were killed in similar attacks, argued they had merely been taking part in an elaborate hoax.

They also argued that the judge's directions to the jury that convicted them for the attempted bombings on July 21 were inadequate and that he had failed to give "clear and tailored" directions.

But three Court of Appeal judges rejected their leave to appeal against conviction and sentence, saying in a joint written statement that the sentences were "utterly justified".

"These were merciless and extreme crimes," they said.

"As they were rightly meant to be, the sentences were severe and extreme. Beyond doubt, however, they were utterly justified."

They added: "On 21 July 2005 London came within a vanishingly short breath of wholesale murder by terrorists.

"The explanation why the date will not be twinned in the annals of its venerable history with the murderous outrage perpetrated on 7 July 2005 is simple: it was sheer good fortune."

The judges rejected the hoax claim, setting out in detail the men's preparations.

They also turned down complaints about the initial judge's directions, saying there was "nothing in this ground of appeal".

"The jury was given appropriate and clear directions on all the issues arising in this trial," the judges said.

"This ground of appeal is unarguable."

Muktah Said Ibrahim, Yassin Hassan Omar, Ramzi Mohammed and Hussein Osman, all Muslims of African origin, were found guilty last July of conspiracy to murder.