The deal covers the three-month period of May, June and July – or while stocks last – and is worth £1,995 for the STi and £1,600 on the WRX.
The Prodrive-developed performance packs are fitted by the dealer after registration and carry the full Subaru three-year/60,000 mile warranty.
It means the Impreza WRX STi Type-UK sees its power rise to 303bhp resulting in a 0-60mph time of 4.6 seconds with a top speed of 155 mph.
Meanwhile, the standard WRX – available in both saloon and 5-door bodystyles – now has 263bhp with a 0-60 mph time of 4.8 seconds.
Both Prodrive Performance Packs include a reprogrammed Electronic Control Unit (ECU) and free-flow exhaust system with a large single rear tailpipe.
The Impreza WRX saloon costs £20,300 with the 5-door at £20,800 while the WRX STi Type-UK is £26,400 (all prices on-the-road).