Relatives of Mark Duggan join families of prisoners who have died in police custody at protest march to Downing Street

Relatives of Mark Duggan joined families of people who have died in police custody today in a protest march to Downing Street which demanded justice for their loved ones.

Mr Duggan's aunt Carole was among the 300 protesters who took part in the annual procession, which started in Trafalgar Square before moving down to Whitehall.

The father-of six was shot dead by a police marksman in August 2011, sparking widespread rioting across London.

Earlier this month his family lost their bid to overturn the verdict in his inquest, which found that he had been lawfully killed.

Other protesters in central London today included the relatives and friends of Sean Rigg who died after being restrained at Brixton police station in August 2008.

Prosecutors have been criticised for a decision not to bring charges against two police officers in connection with the death of the former musician.

Activists also protested over the death of Olaseni Lewis at a south-east London psychiatric hospital in August 2010.

His mother Ajibola said there was yet to be an inquest into the death of her IT graduate son who was being restrained by police shortly before he died.

She called for the Independent Police Complaints Commission to "get a move on" with its investigation and spoke of her "frustration and anger".

She said: "This is happening all the time and it's not just black people, it's Asian and white, men and women. The police have to be held accountable for their actions - if you kill somebody you should be prosecuted."

She added: "This procession brings the issue to the forefront, it's on the internet and television, and the powers that be know that we are watching."

Organised by the United Families and Friends group, the protest marched behind a blue banner which read "No More Deaths In Custody".

Protesters were heard chanting; "Who are the murderers? Police are the murderers".

The procession's starting point coincided with a crowded NFL fan rally in Trafalgar Square ahead of tomorrow's American football game at Wembley between Detroit Lions and Atlanta Falcons.

Deborah Coles, director for the Inquest campaign group, said the procession was an "important but poignant" day for families who had lost loved ones in police custody or immigration detention.

She said: "It is important that the Government realises that this is an ongoing and serious human rights issue. Many families feel betrayed by a system that has let them down.

"The same issues repeat themselves time and again despite the empty platitudes from Government ministers that lessons will be learned.

"This is the last demonstration before the general election and the issue of deaths in custody must be on the political agenda in the run-up to that election."