Relatives and friends of people who died while in police custody have marched to Downing Street to demand justice for their loved ones.
The United Families and Friends group, which organised the event, said about 300 protesters took part in the annual procession, which started in Trafalgar Square and marched down Whitehall.
Activists carried placards which read "No Justice No Peace" and banners in memory of those such as musician Sean Rigg, who died after being restrained at Brixton police station, south London, in August 2008.
Deborah Coles, director for the Inquest campaign group, said the procession was an "important but poignant" day for the families.
She added: "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."
Police and security services are reviewing the security in place around Parliament and other key London institutions after a soldier was shot dead in the Canadian capital Ottawa.
Prime Minister David Cameron has said that meetings were being held to make sure that security and intelligence services have "all the angles covered".
Speaking to the BBC's Asian Network, he said:
British Ebola survivor William Pooley is preparing to return to West Africa to help fight the deadly outbreak.
The volunteer nurse, from Eyke in Suffolk, said he knows that his family and friends will be worried but stressed that there was a urgent need for strong medical support as the virus has claimed almost 4,500 lives, mainly in west Africa.
Mr Pooley, 29, made a special appearance at a training and discussion session in Whitehall for NHS workers who have volunteered to help on the ground with the international effort to combat the spread of the disease.
Mr Pooley, who said he has made a "100%" recovery, added: "I have some experience now of working with Ebola patients so I can apply that.
"My exposure, as with everyone's exposure, was an accident. It is something that everyone will be thinking about - all the volunteers who are here tonight but it is about vigilance really and being cautious. You must never let any complacency creep in."
The Prime Minister will chair a COBRA meeting today to discuss the ongoing epidemic of Ebola in Western Africa.
Ahead of the meeting, the PM spoke to the president of Sierra Leone Ernest Bai Koroma, who said the situation in his country continues to be "very serious".
Downing Street stressed that the meeting in Whitehall was one of a regular series of meetings and had been in the PM's diary for some time.
The UK could face five more years of spending cuts and austerity, regardless of which political party is in power, the outgoing head of the the civil service has said.
Sir Bob Kerslake, who stepped down as head of the home civil service as part of a Whitehall shake-up ordered by David Cameron in July, made the comments in a speech to the Institute for Government think-tank in which he reiterated the need for reform.