Harrow Limmud's ambition in moving to a larger venue paid off as it attracted double the number who came to its last staging two years ago.
A sell-out attendance of 1,000 enjoyed a choice of 134 sessions covering food, film, football and much more at JFS's Kenton premises on Sunday.
"We were thrilled at how the event went," said organising team co-ordinator Helen Levy.
Participants were undeterred by unexpected road closures, on top of sealed-off streets for a local half-marathon. At the 10 o'clock start, a number of classrooms were already sporting "room full" signs, leaving latecomers to find an alternative.
Presenters included Lord Finkelstein, speaking on football, Cambridge autism expert Professor Simon Baron Cohen and Israel's first Bedouin diplomat, Ismail Khaldi, from the Israeli embassy, as well as Board of Deputies presidential candidates Alex Brummer and Jonathan Arkush.
Local MPs Conservative Bob Blackman and Labour's Gareth Thomas, the party's spokesman on the Middle East, also found a way through the traffic to take part in a discussion on antisemitism.
Ms Levy said Harrow Limmud was "one of the largest day Limmuds in the world" - and the only one in London this year.
"Day Limmuds offer an opportunity to those who couldn't attend the [national] conference in December. It's for those who may not want a residential experience and who do not want to, or cannot, travel far." JFS students and staff were among 100 volunteers who shepherded participants to sessions, handed out coffee and ran a children's programme.
Unused food was donated to a local homeless charity.
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