This was the Methodists' Hornsey Road Chapel, built in 1858. It replaced their smaller Chapel built in 1821, which in turn replaced the meeting house on the Hornsey Road the Methodists had been using 1811.
According to their Islington and Camden mission 'while middle-class Wesleyans were moving into the new suburbs, conditions in the area around the original Hornsey Road Chapel were declining. In an attempt to address growing poverty in the neighbourhood, missions were established in Andover Road and Hampden Road. Hornsey Road Chapel was finally closed in 1940, and demolished in 1960 to make way for a police station.'
That means, I think, that it's now Holloway Police Station and looks like this: