The alleged Three Musketeers terror cell have been subjected to "one of the most unfair trials there has ever been in the history of British justice", a defence lawyer has said.

Convicted terrorist Naweed Ali along with three other men from the West Midlands are on trial at the Old Bailey accused of plotting an imminent attack on British soil.

The three-month case, which was partly held in secret, has revolved around the discovery by secret service agents of a JD Sports bag containing a partially-constructed pipe bomb and a large hatchet.

Also found were shotgun cartridges, an imitation handgun with an empty magazine strapped to it and one unfired bullet which could have been used in a semi-automatic pistol, gaffer tape and rubber gloves.

The bag was stashed in Ali's Seat Leon car parked at the Birmingham depot of Hero Couriers, a fake firm operated by undercover officers tasked with infiltrating two of the alleged plotters by offering them delivery shifts.

The prosecution have alleged the discovery on August 26 last year showed the group were in the later stages of planning a terror outrage.

Ali's defence lawyer Stephen Kamlish QC has repeatedly accused the boss of Hero Couriers, undercover officer Vincent, of planting the incriminating evidence before MI5 arrived to bug the car.

In his closing speech to the jury, he alleged police had found "not one shred of evidence of an actual plot".

Mr Kamlish told jurors: "What has happened in this case is you have been sat in on one of the most unfair trials there has ever been in the history of British justice.

"The reason I say that is the prosecution is refusing to investigate whether Vincent planted this bag in the car simply because he is a police officer."

Mr Kamlish accused prosecutor Gareth Patterson QC of acting like Vincent's defence counsel and being fair to all the other prosecution witnesses, but he "did not once mention being fair to the defendants in this trial".

He went on: "They have not because they are refusing to investigate the main thing to investigate in this case.

"Mr Patterson says there is no duty to investigate unreasonably. Investigate whether Vincent bought cartridges, an air pistol, hatchet. This is not rocket science.

"The reason they have not done it is they are scared of finding out the truth. They are protecting their own. Even witnesses are being forced - probably by bullying - to lie."

He added: "I know I'm like the dog you want to muzzle - but I'm fighting for my client's life here."

Mr Kamlish listed 16 things he said the police should have investigated, including checking Vincent's alleged shotgun licence for cartridge purchases and whether he owned a 9mm self-loading pistol.

He said police should also have checked the five branches of JD Sports in the Birmingham area to find out whether Vincent had been to any of them.

Ali, 29, and Khobaib Hussain, 25, both of Sparkhill in Birmingham, and Mohibur Rahman, 32, and Tahir Aziz, 38, of Stoke-on-Trent, deny preparing terrorist acts. The trial continues.