Large 500ml bottles of Aussie Beach Mate Shampoo and 400ml Aussie Beach Mate Conditioner only £2.48 at Superdrug on-line. (not sure if the same in-store**). Free delivery (or collect from a store) if you have their Beautycard, and no minimum spend either! I think this brand used to be called 'Aussie Miracle'
It doesn't say it's an offer price (possibly a glitch??), but the smaller 300ml size shampoo is £4.69 and 250ml conditioner is £4.19 - both part of the selected Aussie 2 for £7 offer
** Update 5.11.16: Conditioner priced @ £5.99 in-store (Birkenhead)