Plans for the school were put forward by members of the Christian, Jewish, Hindu and Muslim faiths - with Sikh support - at a meeting in the House of Lords on Monday.
The faiths would collaborate to run the school, which would either be one of the Government's new city academies - privately-sponsored state schools, independent of councils - or have voluntary-aided status like church schools. Talks are being held with a London borough where the school could be sited.
Meanwhile, plans to bring together Catholic pupils and those of other faiths in an Edinburgh suburb are being fought by Catholic parents.
The local authority, Midlothian, wants to replace two run-down schools in Dalkieth - Jone Roman Catholic, the other non-denominational - Jwith two new schools sharing some facilities, such as a canteen and assembly hall. But Catholic parents do not want their children to mix freely with others. Some fear they may see unsuitable material, such as contraception advice.