Home Secretary Theresa May has said the government is doing everything possible to counter extremist groups operating in Britain.

Speaking at the Community Security Trust annual dinner in central London on Wednesday evening, Mrs May said more would be done to stop extremists "masquerading as charities" in order to raise funds.

Mrs May praised the Charity Commission's efforts to take a "more effective and aggressive line in seeking out and ejecting" such organisations.

"Too often organisations whose purposes have been the opposite of charitable - and which have even been involved in sending money to straightforwardly terrorist organisations - have been allowed to flourish as charities," said the Home Secretary.

But she warned that the "battle against intolerance and extremism, and the murderous violence it spawns, is not going to end soon".

"Ultimately, the best way to fight extremism is to counter its ideology. We have to convince everyone that the extremists are utterly wrong. We have to persuade people that our values – the values of toleration, of freedom, of equality before the law of every individual – are better."

Mrs May said 1920s Germany had provided a "stark and terrible warning" of what can happen if hate speech is "normalised" and becomes part of mainstream conversation.

"That is why we have to continue to fight it and to do everything we can to ensure that it is restricted to the margins. We must never again allow hatred to seep into public discourse."

The dinner was attended by more than 1,000 guests including 60 MPs, two Cabinet ministers - Eric Pickles and Dominic Grieve - and 50 senior police officers.

Tributes and presentations were made in the name of the late David Brecher, a founding trustee of CST and its legal adviser, who died last October, and to the outgoing Chief Rabbi, Lord Sacks.

Lord Sacks, who has his own personal CST protection team, joked that throughout the years "they have kept me safe from the community and kept the community safe from me."

CST founder Gerald Ronson made a tough fundraising appeal. He said: "They tell us that they don't hate Jews for being Jewish - they only hate those of us who are Zionists. As if this means you should be condemned as a racist or some kind of monster, who needs removing from society. Were the children in Toulouse Zionists?

"In their ivory towers, some people call this 'the new antisemitism'. It doesn't look very new to me."