For 2003 all three main manufacturers in the premier Touring class ran three cars. Reigning champions Vauxhall cut down to three Astra Coupes by axing its Egg Sport squad and entering three VX Racing-liveried cars, run once again by Triple 8. 2002 champion James Thompson and runner-up Yvan Muller remained, and Paul O'Neill moved across from Egg Sport to take the third seat. MG expanded to three West Surrey Racing-run ZSs, with Colin Turkington joining 2002 drivers Anthony Reid and Warren Hughes after impressing in his debut season with the Team Atomic Kitten MG squad, which had also been run by WSR.
Arena Motorsport ran three Civic Type Rs for Honda, with only Irishman Alan Morrison remaining from the 2002 line-up. Matt Neal replaced Andy Priaulx (who left to contest the European Touring Car Championship with BMW) after moving from Vauxhall, and teenager Tom Chilton filled the third seat after an impressive debut year in the Barwell Motorsport-run Astra. Proton again returned as a fourth manufacturer, retaining both David Leslie and Phil Bennett in its two Impians.
Vic Lee Racing again served as Peugeot's representative on the grid (although the marque pulled its factory support at the end of 2001), entering two newly built 307s for Dan Eaves, who had contested both 2001 and 2002 for the team, and Carl Breeze, who joined the team mid-way through 2002. Production class champions Synchro Motorsport made the step up to the top class with champion driver James Kaye running an ex-works Honda Civic Type R, as did Rob Collard with his self-run team, entering an ex-works Vauxhall Astra Coupe, and GA Motorsports with Gavin Pyper racing a similar machine. Pyper ran out of funding mid-way through the season, resulting in Breeze switching from VLR to replace him and Paul Wallace being called up from GA's Production class squad to drive a second Astra, previously raced as a one-off by Gareth Howell. Howell himself later appeared in another ex-Triple 8 Astra for Team Dynamics. Renault Clio Cup graduate Daniel Buxton took over Breeze's driving duties at VLR.
Barwell Motorsport headed the Production class field after stepping back down from the Touring class and acquiring Synchro Motorsport's title winning Honda Civic Type Rs, which were driven by young debutante Luke Hines, and Alan Blencowe, moving from GA Motorsports. Edenbridge Racing cut down to a single BMW 320i for single seater convert Michael Bentwood, with Tom Boardman switching to John Batchelor's team (now known as Team Varta) in a new Peugeot 307. Jim Edwards Jnr returned in a Honda Accord as the team's second driver. A Peugeot 306 GTi and a second 307 joined the Varta line-up mid-way through the season together with Jay Wheals and Richard Marsh, and each of the four drivers raced more than one of these chassis across the remainder of the year.
GA Motorsport campaigned Alfa Romeo 156s for a fourth year, with Chris Ryan and Paul Wallace driving. However, Ryan withdrew after an expensive crash in the second round at Brands Hatch, and Wallace was called up to the team's Touring class assault mid-season. Mark Fullalove joined the grid mid-season with his own team, driving the Peugeot 306 he had raced for Tech-Speed Motorsport in 2002, while Jason Hughes was another late entry in a Nissan Primera run by his own Kartworld Racing team.
Note: bold signifies pole position in class (1 point awarded in first race only), italics signifies fastest lap in class (1 point awarded all races) and * signifies at least one lap in the lead (1 point given all races).