The Oxford Centre for Hindu Studies is gathering a Hindu archive which explores Hindu influence in Britain and beyond.
Hindu heritage sites include The Maharajah's Well in Berkhire, the tomb of Rammohun Roy in Bristol and the Chattri near Brighton (which is dedicated to Sikh and Hindu soldiers who were cremated there).
The first Indian restaurant in England was opened in 1810 by Sake Dean Mohamed. The oldest surviving Indian restaurant, Veeraswamy, was opened in 1926.
Some information on Muslim heritage, including blue plaques and old mosques, can be found on the British Muslim heritage site. A history of Muslim science is on the Muslim Heritage website.
Sikh heritage in Britain is celebrated on the Anglo Sikh Heritage Trail website.
The BBC has some information on Buddhism in Britain.
The Institute of Jainology has a list of Jain temples in the UK.
Jewish heritage can be explored on the Jewish trails website.
Inspired by the Jewish trails site, I also started a Pagan trails website, which needs contributions.
There's a Unitarian heritage trail in London. Also the Humanist Heritage website mentions several Unitarian sites connected with the early history of Humanism. The Unitarian Communications blog has now gathered a list of Unitarian heritage websites.