You will have to find a very flexible dealership to allow full payment or even significant payment on a credit card (or a series of credit cards). Most have a limit of less than £1000, enough to cover a small deposit or a largeish privately paid service repair bill. My local dealership had a strict policy of £800 max payment by credit card.
The credit card companies want a 3 to 5% chunk of every purchase you make on it. You bought something from Argos for £100 on your Mastercard? Argos saw about £96.50 of it. That’s £780 (3%) to £1300 (5%) margin lost on a £26k car that may have already been generously discounted.
With £26k loaded onto credit card debt, you might find your credit rating takes a bit of a hiding if you then plan to take out other loans to pay off the credit cards once the 0% period runs out, or they strictly stick to babalnce transfers rather than 0% purchases.
Noexcuses: Seems a lot of pissing about for £75 gain. Why not chuck your £15k cash at the car, owe £10k and put that £10k on the cards to enjoy 0%/1.5% paid over the year. If you’ve got £417 spare a month for payments then you could be in a position to only owe £5k after 12 months when the CC 0% deal on purchases is likely to have run out. You’re also far more likely to be able to get £10k on CC debt than £26k, and it will look better for you on your credit rating. If you start applying for umpteen cards all at once, your credit rating will go down for a month or 2 after every application.