Gerry will sub, I think of 2 obvious candidates to play before him:
Frank Turner and the sleeping souls: Frank played R&L for 10 years in a row but has now missed the last 3. He will surely return at some point and playing 3rd down makes sense.
DMAs: Maybe a slight stretch to put them 3rd but they are playing Brixton and Ally Pally this year which puts them on par with 3rd down regulars like the Vaccines, Blossoms and the Wombats. With LG and Gerry playing, the dark fruits brigade will be out in force on day tickets so adding DMAs would make sense.