CAMDEN TOWN — An historic Spiritualist temple is under threat from developers. The building, whose foundation stone was laid by Sherlock Holmes’ author and noted Spiritualist Sir Arthur Conan Doyle, has become the subject of a debate spurred by a new proposal by development group UrbanLab. The company reportedly seeks to demolish the 90-year-old temple and replace it with nine flats and a gallery. The building is currently owned by the Spiritualists’ National Union, which owns 350 spiritualist churches across the country. The Rochester Square temple is particularly historic.