ASDA watford has a mountain of this, believed nationwide,
cant go wrong at this price it was £7 in the winter then recently down to £5. at £2 its well worth stocking up on and can be used at half strength for summer
i.e half water half screen-wash
has their own brand of "Rain-X" stuff in it which is a bonus
yes I know it only goes down to -10c but that's going to be fine for 90% of the year and is far better than most.
Prestone® De- Icer Windshield Washer Fluid De-Icer with Dirt Blocker is specifically engineered to improve winter driving visibility. Using Prestone® De-Icer Washer Fluid helps clear light ice and frost and helps prevent dangerous re-freeze from forming on your windshield. Our Dirt Blocker formula improves your total winter driving visibility by helping to repel the build-up of dirt and salt from road spray as you drive. Get clearer glass and enhanced visibility for longer periods of time.
Use at full strength. Add directly to washer fluid resevoir. Make sure to wash exposed skin thoroughly with soap and water after each use.
De-Icer’s high methanol content ensures strong ice melting power and the addition of ethylene glycol helps prevent dangerous re-freeze from forming on windshields.
Prestone’s Dirt Blocker technology coats windshields with a resilient organo-modified siloxane copolymer. This formulation imparts a durable hydrophobic surface on the windshield that helps prevent road spray from adhering to windshield glass by moving dirt particles away from the windshield surface and into the washer fluid that beads and rolls off the glass.