Charlene (left) and Letisha died in a botched gang attack

Errol Robinson - acting for Marcus Ellis and Rodrigo Simms - says the way witnesses' identities were protected has led to a miscarriage of justice.

One key witness was given a false name, hidden behind a screen and had his voice altered electronically.

The Crown Prosecution Service said the measures were due to fears of reprisal.

It said the trial, at Leicester Crown Court, had been marred by serious and consistent attempts to intimidate key witnesses.

'Botched attack'

Letisha, 17, and Charlene, 18, were shot outside a party in Aston, Birmingham, on 2 January 2003 in what the jury was told was a botched gang attack.

Charlene's half-brother Marcus Ellis, 24, Michael Gregory, 22, Nathan Martin, 26, and 20-year-old Rodrigo Simms had denied the murders but were found guilty on Friday.

A fifth defendant, Jermaine Carty, was cleared of possessing a firearm on the night of the shooting.

The men were all convicted by majority verdicts, with the exception of Ellis, who was convicted unanimously.

They will be sentenced on Monday.

Mr Robinson confirmed that his clients would appeal. A solicitor for Gregory said he anticipated that his client would also appeal, while Martin's solicitor declined to comment.

During the trial, the defendants' barristers continually expressed concerns that prosecution witnesses had been allowed to give evidence anonymously.

There has been a grave miscarriage of justice following one of the most unfair trials of modern times Errol Robinson Defence solicitor

One of the main witnesses - a known criminal - was granted total anonymity during the trial, with only the prosecution and judge knowing his true identity.

Known only by the false name of Mark Brown, he became a "pseunonymous" witness - a phrase coined at the start of the trial.

In his summing up to the jury, Nigel Rumfitt QC, defending Marcus Ellis, argued: "As far as we are aware, no witness has ever been allowed to give evidence in the way Brown was in the entire history of our common law going back the best part of 1,000 years."

Witnesses 'afraid'

Mr Robinson said: "There has been a grave miscarriage of justice following one of the most unfair trials of modern times.

"If someone is accusing you of anything, let alone a matter of this gravity, you really ought to know who that person is so you can investigate the motives for that person giving evidence so that there is a fair trial."

He said the appeal could go beyond the domestic court to the European Court of Appeal.

"The European Court does not encourage people being convicted mainly on the evidence of an anonymous witness. That is sensible and the precedent set in this trial should not be adopted."

David Blundell, chief crown prosecutor for the West Midlands, said: "One of the things police had to address was how we could persuade witnesses who had seen or heard relevant evidence to come forward. Witnesses were not prepared to give evidence without protection."

The convictions were welcomed by Liberal Democrats president Simon Hughes at the party's regional conference at the University of Birmingham on Saturday.

He paid tribute to the memory of Charlene Ellis and Letisha Shakespeare, and said: "I congratulate all concerned in bringing their killers to justice.