The manufacturers warranty is 3 years. Any work carried out in this time has a 1 year warranty, or until the end of the manufacturers warranty expires. Which ever is longer.
As for complete rejection, that’s a difficult scenario. The length of time you’ve had the vehicle goes against you, as you’ve had more than enough time to reject the car, whilst pump 1 and 2 were failing. The better option for you is to go for a partial rejection. This is monetary compensation for the difference in what you bargained for when buying the car, “a working hippo” v what you’ve actually got, “an unhappy hippo”. Less than 5k value and this can go through the small claims court. Be aware you can loose, and have to pay costs. They have the option to counter claim against you, or fight the action.
Write to your dealer first, briefly outlining the problems and set them a reasonable time limit on what you want them to do. Warn them that if they don’t carry out your wish, then you are prepared to tale this further. Be polite. Keep it factual. Don’t though in “not fair because…” and “I think…” Be precise and straight to the point. Don’t explain the law to them. Tell them as above. What you want and a time limit.
Any legal action you take as a buyer is against the seller, not the manufacturer. You can’t sue the manufacturer over a warranty, as there is no contract in place. This has never been done with a car manufacturer in the UK.
This is not definitive legal advice. You should pay for proper legal advise on your won circumstances. I would suggest to save wasting time you get legal advice prior to going further. If the dealer rolls over and sorts the problem out without hassle, then your lucky. Failing that the litigation route is VERY stressful.
Consumer rights : Directgov - Government, citizens and rights