I saw (and bought) several 250ml (regular sized )Trevor Sorbie products from my local Poundland in Rotherham Retail Park; looking at the official website, the range has changed to different bottles alongside shedding some of the products i.e. the colour+ range (I use the redhead shampoo and it keeps the colour vibrant for longer!), hence its presence in a poundshop I believe!
This range normally retails between £4.50 and £6 a bottle (Boots, where I normally buy it from), don't know if this is national or just local, but surely worth some heat? ;)