The lost church of Saint Gabriel Fenchurch is unusual as it has had three different names in the past. The earliest reference is from the 13th century under the name All Hallows Fenchurch, but between the 13th and 16th century, it seems to have been called St Mary Fenchurch and it is not until 1526 and onwards that it was referred to as St Gabriel Fenchurch. The 17th century historian Richard Newcourt (who published a history of the Diocese of London in 1708) was the first to identify that these names all referred to the same church. It stood right in the middle of Fenchurch Street between Mincing Lane and Rood Lane and is clearly visible on the Copperplate map of 1555.
It may be that the church always had a triple dedication to All Hallows, St Mary and St Gabriel or maybe the names were added as the church was enlarged or rebuilt. We do know that some rebuilding took place in 1631 but the benefits were short-lived as it burnt down some 30 years later in the Great Fire of London. It was decided not to rebuild the church, maybe because its position was a awkward one – blocking a major city thoroughfare. The parish was combined with the nearby church of St Margaret Pattens.
If you are searching for remains of the church today you will find a blue plaque in Fenchurch St near where the church stood. Also a pew in St Margaret Pattens is marked “St. G.F “ to indicate that it was reserved for parishioners of the church that burnt down. You can still find the old graveyard of St Gabriel Fenchurch a little distance away in Fen Court. It has been paved over and turned into a public garden.
the wikipedia page for St Gabriel Fenchurch is here