5 R(ex) and IT inside (Man) RAY, a US artist who mostly worked in Paris
20 weak clue FORTY NINE is a square, followed by close to trafalgaR
15 LEMON - fruit, GRASS - shop as in "tell on", ingredient in Asian (Thai especially) cooking)
1da SPEAR CARRIER is an extra in a film or play who doesn't get to say anything. No idea what it has to do withBarrow, though.