Halfords have all of their 'Simoniz' car washing items on Buy One Get One Free.
I picked up TEN LITRES of the shampoo for just £10!
I wasn't too sure about buying Simoniz, as I'd never heard of them, but it's FAR FAR FAR better than the 'Car Plan' and 'TripleWax' stuff out there, and the same price!
That's coming from someone who washes their car, and the difference is immense!
(Btw, I know you can get 5 litres for £5 at Costco, but not everyone has access to a Costco card)
Available to reserve online for pick up in store, or you can purchase online and have it sent to you. Not sure on postage costs.
Hope this is of help to someone!
Just noticed a 15% discount code! D'oh!