The warranty that they gave ya when ya bought tha car is valid regardless of whether or not the dealer still operates. Check the paperwork that ya have and let me know what it says regarding warranty as in who was responsible for it's inception. If it is still valid within the date from sale then your still gonna be entitled to a minimum of £40 per hour labour of upto around 8 hours and maybe around £600 in parts per claim within a usual period of a minimum of 3 months.
There should also be a contact number for the warranty underwriters in the paperwork. If it's just a company name then get back to me and I will check on my database for ya. The warranty is open to any Garage that is VAT registered and willing to carry out the work, not necessary for you to take it to the dealer that you bought the car off in the first place, it is an insurance policy just like the one that covers you for accidents.