LONDON (Reuters) - A Ghanaian man was sentenced to 33 years jail on Tuesday for helping to plot al Qaeda-inspired botched suicide attacks on London's transport system on July 21, 2005.

Manfo Kwaku Asiedu was sentenced at Kingston Crown Court after earlier admitting a charge of conspiracy to cause explosions over the failed bombings.

The attacks were attempted two weeks after four British Islamists killed 52 people in suicide bombings on three underground trains and a bus in the capital.

Four men -- Muktah Said Ibrahim, Yassin Hassan Omar, Ramzi Mohammed and Hussein Osman -- tried to detonate hydrogen peroxide-based bombs on July 21, but their homemade devices failed to explode and no one was killed.

They were all jailed in July for a minimum of 40 years but a jury failed to reach a verdict against Asiedu and another man, Adel Yahya.

Yahya was jailed for nearly seven years earlier this month after pleading guilty to a lesser offence.

Asiedu had been due to face a re-trial but pleaded guilty at the Old Bailey on November 9.

He was supposed to be carrying a fifth bomb on the day but ended up dumping the rucksack with his device in a park in north London. He denied losing his nerve and said he just wanted to get rid of the bomb.

A few days after the failed attacks he handed himself into police and admitted in court that he then lied to detectives on an "epic scale".

During the trial he dramatically turned on his co-conspirators, contradicting their defence that the plot was a hoax, designed as a publicity stunt, meaning he had to be seated separately from the other accused in the dock.

His lawyer said that Asiedu had returned to the flat where the bombs were made to remove the hydrogen peroxide and added his client had dismantled a booby-trapped sideboard which could have destroyed the entire apartment block.

The basis of Asiedu's guilty plea was that he had bought the hydrogen peroxide for the bombs, his lawyer said.

After sentencing, Deputy Assistant Commissioner Peter Clarke, head of the Counter Terrorism Command with the Metropolitan Police and National Co-ordinator of Terrorist Investigations, said Asiedu was a "dedicated terrorist".

"Asiedu was one of the terrorists who wanted to bring a fresh wave of carnage to London on 21st July 2005, just two weeks after 52 members of the public had been killed by terrorists," he said in a statement.

"He is a dedicated terrorist who consistently lied about the role he played in this plot. Only now, has he finally admitted his guilt.

"Asiedu is the latest in what is becoming a long line of terrorists pleading guilty to their offences. This shows the scale of the threat we are facing and the strength of the evidence we are putting before the courts."

He urged the public to remain vigilant.