More than 1,200 people including Holocaust survivors, religious leaders and politicians have attended Britain's national Yom Hashoah commemoration in central London. 

Today's event took place at the Holocaust Memorial in Hyde Park, and featured speeches, candle lightings and musical interludes. 

Sadiq Khan, Mayor of London, Chief Rabbi Ephraim Mirvis and Mark Regev, Israel's ambassador to Britain, all addressed the crowd under grey skies in the park. 

The hour-long ceremony opened with remarks from Henry Grunwald, who told the crowd the theme of this year's memorial was "defiance". This week marks the 75th anniversary of the Warsaw ghetto uprising and today is the 73rd anniversary of the liberation of Bergen-Belsen. 

A statement was read out on behalf of Shoah survivors by Gena Turgel, who, amid total silence from the crowd, described how she survived an Auschwitz gas chamber. 

There was loud applause as Rabbi Mirvis called on Europe's political leaders to condemn contemporary antisemitism. 

"The call of the hour is for strong and solid leadership to take on antisemitism and send out the right tone of message... to get rid of this evil in our society," he said. 

"Every political leader must send a clear and unequivocal message that it will not be tolerated any more."

Memorial candles were lit to remember those who died in the Shoah - with communal leaders and children accompanying survivors to light them. 

With the temporary seating erected in the park packed, there was a moving moment as the huge crowd recited Kaddish in unison. A minute's silence was broken by Rabbi Barry Marcus blowing the shofar. 

Mr Khan said it was "vital to take time out of our lives to remember, to reflect and to recommit that our children will learn about the dangers of where prejudice and hatred can lead".

He said the world was living through "uncertain times" and one of the "difficult lessons we must all learn" was that peace was not an automatic right. "If we are not careful we can go backwards," he warned. 

The Mayor added: "Jewish communities in this country, in this city, are feeling unsafe. This is completely unacceptable. It must not go unchecked. We must all remain defiant...in our mission to learn the lessons of the past."

Mr Regev said: "Could it be that some people have a problem with the fact Jews refuse to be victims anymore? 

"We are once again a free and sovereign people in our homeland. To those who call for Israel's destruction... we will protect ourselves and we will continue to call out those who turn a blind eye in face of anti-Jewish bigotry. When the Jewish people say 'never again', we mean never again."