Boris Johnson and Tony Blair have lauded the interfaith aspect of Mitzvah Day.
Mitzvah Day marks the start of the national Interfaith Week and Mr Blair praised the notion of "Jews working with Christians, Muslims, Hindus, Sikhs and Baha'is to go out into their communities to help clean up the area".
Mr Johnson said such co-operation was a "fantastic example of what can happen when people put in a little time and a little thought into doing something for others".
One of the activities run by Alyth Synagogue in Golders Green was a brunch for refugees and asylum seekers.
Organised by the shul's head of social justice, Nikki Levitan, it featured children's activities, as well as hosting the Habonim Dror Refugee Bike project, which restores old bikes for refugees.
"In the 1930s, our community held brunches for German-Jewish refugees," Rabbi Mark Goldsmith pointed out. "We want this to be something that carries on."
Among those at the brunch was Sudanese refugee Annour Izzadine, who said: "Integration is really important to me.
"It's good to know each other and I hope the friendship can benefit everyone here."
Mitzvah Day interfaith chair Daniella Pears is determined to forge a relationship between her synagogue, South Hampstead, and the London Central Mosque for Mitzvah Day 2012.
This year, 70 South Hampstead members visited the mosque to view its Interfaith Week exhibition.
"I was thrilled at the number of people who wanted to go," Ms Pears reported.
Mosques, community centres and synagogues were encouraged to run joint social action projects.
Mitzvah Day founder Laura Marks believes that many communities want to get involved in interfaith work, "but it can just be people sat around eating samosas.
"Social action is the perfect way of getting people doing something active together."
Brondesbury Park Synagogue held a joint food drive with members of the Al-Kohei Islamic Centre at Sainsbury's in Willesden Green in aid of the local St Mungo's shelters for the homeless.
Younis Hafidh, 16, said: "As soon as I heard about the volunteering, I thought it would be good to get involved. It's a great cause."
North London Reform congregants joined forces with Palmers Green Mosque members for a shopping collection.
And in Leicester, Jews, Christians, Hindus, Muslims and Sikhs collected toiletries outside three supermarkets for domestic violence victims living in safe houses.