Human rights campaigner Peter Tatchell was ejected from Thursday's Holocaust service at Westminster after protesting against Conservative asylum proposals.
Mr Tatchell denied his protest at the commemoration was inappropriate
Mr Tatchell said he had shouted "never again, today means not closing our doors to refugees fleeing persecution".
Scotland Yard said he was detained and escorted from Westminster Hall but he was not arrested.
The service marked 60 years since the liberation of Auschwitz, where over 1m people were killed under the Nazis.
The Nazis' final assault on the Jews from 1933-1945
Estimated 15m civilians killed by regime
6m Jews murdered
1942: Gas chambers built at Birkenau concentration camp, mass transports begin
Majority who arrive gassed immediately
About 900,000 gassed at Birkenau
Over 1.1m died at Auschwitz-Birkenau and its sub-camps
1m of them were Jewish
Altogether some 15 million civilians are thought to have been murdered by the regime, some six million of whom were Jewish.
The event at Westminster Hall was attended by hundreds of holocaust survivors and veterans of World War II.
Mr Tatchell attended as an officially invited guest.
He denied his protest disrupted the service, saying he waited until the commemoration ended and the Queen and prime minister had left.
He then shouted: "Don't let Michael Howard dishonour the victims of the Holocaust with his quotas for asylum seekers."
This week, Mr Howard unveiled the Conservatives' immigration policy which includes an annual limit on asylum.
Under the proposals all claims would also be processed overseas at United Nations refugee camps.
Mr Howard said his party's plans to cut immigration were not racist, arguing they would make the asylum system fairer for genuine refugees.
Mr Tatchell said his protest against the policy was appropriate: "It is hypocritical to remember the Jewish victims of the 1930s, while ignoring Tory plans to deny asylum to people fleeing persecution today."
Other Holocaust commemorations took place around the world, with the leaders of 37 countries attending a memorial service at Auschwitz itself in Poland.
Foreign Secretary Jack Straw and Prince Edward led the UK delegation, which included three British survivors, to the former concentration camp.