For two decades, the iconic image of Stephen Lawrence has looked out at us from the TV and newspapers. It was a murder that was described as "scarring the conscience of the nation" and led to formal inquiries into institutional racism in the police after apparent mishandling of the investigation. As a result there have been 20 years of soul-searching about race relations and campaigns tackling racial discrimination.

The 18-year-old was murdered in a racially-motivated attack in south-east London on 22 April 1993. Gary Dobson and David Norris were jailed for the teenager's murder last year.

Yesterday at a special 20th anniversary memorial service of her son's death, the mother of Stephen, Doreen Lawrence, said: "I've always tried to look forward and to focus on the positive since Stephen's murder, and looked to see how I can make the lives of others better. My pain is raw and that of my children.”

Friends, relatives and supporters of the charitable trust set up in his name attended the memorial service near Trafalgar Square.

Described as a moment of reflection and a chance to confront inequalities in our justice system, the Stephen Lawrence case was a defining moment.

Dr R David Muir, a former deputy chair of the Metropolitan Police Association, former chair of the MET Diversity Recruitment Taskforce and former director at the Evangelical Alliance, said: “The Stephen Lawrence inquiry was a catalyst and a defining moment in bringing about significant changes in the police service and the wider public institutions.

“There is always more to be done and that is why we need to ensure that the police service continues to recruit, retain and promote more black and ethnic minority officers.

“As a result of the Stephen Lawrence Inquiry churches have made tremendous effort to engage with the police in their local communities. Groups like Streets Pastors and the Peace Alliance are good examples of this engagement to reduce crime and support community cohesion. In addition, we have seen church leaders participating in local police independent advisory groups.”

The prime minister said that there has been a change in culture in not accepting racism in our country but critics point to controversial statistics of the increased rate of stop and search among black men.

Dr John Sentamu, Archbishop of York and advisor to the inquiry, said: “As we remember Stephen’s death at this time we need to renew our determination to rid our communities of racism, hatred, fear, ignorance, stereotyping, and the advantaging or disadvantaging of others because of their colour or ethnic origin.

“The elimination of racism remains a serious task for all of us. We may congratulate ourselves that it has been eradicated in one place and we can relax, but sadly it often turns up somewhere else, with slightly different characteristics – this time perhaps focused on asylum seekers, or eastern European workers. Wherever it is found it must be fought.”

The Stephen Lawrence Charitable Trust set up in his memory by his family continues to promote justice and opportunity for young people.

20 years on, do you think Britain is more or less racist than then? Vote in our poll of the week