New London mayor Sadiq Khan said on Wednesday that he was not a Muslim leader but represented everyone in the city, after making history by becoming the first mayor of his faith in a major Western capital.

"Let me be very clear, I'm not a Muslim leader or Muslims' spokesperson, I'm the mayor of London. I speak for all Londoners," the 45-year-old said in a wide-ranging media briefing.

Khan, the son of Pakistani immigrants, added however that his election proved "that it's possible to be Muslim and a Westerner. Western values are compatible with Islam".

He repeated his criticism of presumptive US Republican presidential nominee Donald Trump, who has proposed banning all Muslims from entering the US.

Khan, a member of Britain's opposition Labour party, said Trump was "ignorant about Islam" and was "playing into the hands of the extremists".

Trump made the proposal in December, days after a terror attack killed 14 people in San Bernardino, California, saying Muslims should not be able to enter the US "until our country's representatives can figure out what is going on."

Khan also repeated his support for Britain to stay in the European Union in the June 23 referendum, saying membership was crucial for London's prosperity.

"It's crucial for London to remain in the EU... Half a million jobs are directly dependant on the union," he said.

He added that Paris mayor Anne Hidalgo at their meeting on Tuesday had joked that in case of Brexit, she "roll out the red carpet to welcome London companies" to the French capital.

He said he would be happy to campaign alongside Conservative Prime Minister David Cameron "because it's more important than political parties".

The latest census showed that 12.4% of Londoners are Muslim, 48.4% Christian, 1.8% Jewish and 20.7% have no faith.

The British capital's Muslim community is hugely varied, covering multiple ethnic and social backgrounds as well as a variety of moderate and traditionalist views.