Chief Rabbi Lord Sacks has backed the plan for a Jewish secondary school in Leeds, which is opposed by Manchester's King David High.
More than 150 Leeds parents support the free school proposal, which Lord Sacks sees as a means "to ultimately secure the Jewish future". But KD, which has 100 pupils from Leeds, argues that a Leeds school would "damage both of us".
Simultaneous applications to the government's free school scheme and a local authority voluntary-aided pathway are being sought by Leeds's Brodetsky Primary School to ensure that secondary provision starts from 2013. A letter of support from Lord Sacks is included in the documentation for both applications.
Brodetsky head, Jeremy Dunford, who would also lead the secondary school, has urged the Leeds community not to rely on Jewish schooling in Manchester.
He cited a meeting he had attended at which the Chief Rabbi spoke about the viability of Jewish schools.
"He was asked directly if the increasing number of Jewish schools is sustainable with the current size of the UK community," Mr Dunford said. "His response was very clear. Historically, the concern had been there were not enough Jewish schools. Why now complain if we have too many?
"We are in the fortunate position to be able to plan a small high school that fits the size of the community."
Reaffirming support for the Leeds project this week, Lord Sacks said "Jewish education has always been the beating pulse of Jewish life and a priority area of investment for our community. A secondary school in Leeds will strengthen Jewish education in the city and help to ultimately secure the Jewish future."