Solution to Gravest by Stick Insect

 Solution to Gravest by Stick Insect

Initial grid

Final grid

First and last letters of clues give IN TITLE REPLACE ONE CLUE ANSWER WITH ITS NUMBER TO SHOW ADDRESS and CHANGE A LETTER IN EACH OF TEN ANSWERS. HIGHLIGHT PAST RESIDENTS.  Inserting Ten Down for “rave” in the title indicates TEN DOWN IN G ST.  The final grid shows ten prime ministers, past residents of 10 Downing St.