Have you been able to identify the area/s he's been spraying? if so you can clean down with a solution of biological washing powder and water (ok to used on painted walls, skirtings, be careful with furniture though - especially veneered furniture if it gets too damp, veneer wil come off!) Don't forget to use the solution on carpets too if you have them - below the area where he's sprayed, as some will inevitably drip down. After everything is dry again, give a light spray with surgical spirit to remove any last traces of smell that might attract him back - finally, use the Feliway spray in the areas, and hope that does the trick! You need to use the feliway spray daily until he's not spraying any of the areas anymore.
Presume he's neutered? and are you sure its Thomas who is spraying? - have you got a cat flap, if so could the new cat be coming in and spraying?