Demon Tweeks are currently offering a circa 17-20% discount (Approx £50 off) the Superchips Bluefin remapping tool + Remap. They are also including a free K&N Air Filter relevant to your car (usually worth £30). No discount codes needed.
The Bluefin tool allows you to apply and remove a professional provided remap from Superchips to your car within 10 minutes rather than taking it to their office.
Gains very by engine however they are promising improvements in BHP, Torque and fuel consumption for diesel engines.
See here http://www.superchips.co.uk/s/how-it-works
I know these aren't for everyone and I'm hoping not to open up the remap vs tuning box debate. But I am just pointing out that you can get the Bluefin cheaper from Demon Tweeks rather than direct from Superchips, plus you also receive a K&N air filter for free (usually £30 - £50).
Potential 6% cashbach via topcashback also