The trust wants to challenge people to imagine the unimaginable

Multi-faith ceremonies, talks, dramatic performances, concerts, guided walks and film screenings are taking place in many of the capital's boroughs.

Commemorative multi-faith services are to be held in Barnet, Haringey, Lewisham, Tower Hamlets and Romford.

Events in other areas will continue until Friday to remind people about the millions of victims of Nazi persecution and other genocides since then.

Chris Shaw, chief executive of the Holocaust Memorial Day Trust, said: "It is quite established within schools to learn about the Holocaust, but we're beginning to think it is the slightly older people who know less."

We're beginning to think it is the slightly older people who know less Chris Shaw

She said people aged between 18 and 40 may not have learnt about the holocaust in school, but older people had a "more immediate link" with the experiences during World War II.

The trust, which runs the national commemoration event, has made this year's theme Imagine - Remember, Reflect, React, to challenge people to imagine the unimaginable.

Its website states: "It [the theme] asks us to focus on the lives and experience of victims and survivors of the Holocaust; of Nazi persecution and of other genocides.

"It marvels at the resilience of enterprise, culture and of life itself in the face of destruction."

A guided walk from Aldgate to the Nelson Street Synagogue will feature stories on the lives of prominent East End Holocaust survivors.

An exhibition of paintings and stained glass by Moshe Gallili, a Holocaust survivor, is being held in Enfield and a documentary on the Mauthausen concentration camp in Austria will be screened in Norfolk Place.