Got a leaflet through the door and went to my local store in Northampton who honoured the deal. Buy the Nikwax TX Direct Wash for £9.99 and get the the Tech Wash free, worth £6.99! Ideal, as I need to wash my North Face jacket which will help maintain its condition it once was.
Doesn't appear to be online so I guess the deal is in-store only.
Use TX Direct for all your weatherproof gear including Gore-Tex®, Sympatex and eVENT® - in fact anything that is designed to keep the water out and maintain breathability, unless it has a wicking lining. The treatment adds or renews water repellency and revives breathability so that your gear performs better and lasts longer. Being a wash-in treatment you can be confident that the entire garment is immersed and no areas are missed.
Tech Wash is a wash-in cleaner for waterproof clothing and equipment such as nylon and synthetic tents, awnings and rucksacks. It revitalises breathability and water repellency without damaging Durable Water Repellent coatings, as well as removing detergent residues from previous washes - essential when preparing kit for reproofing. It is water based, environmentally friendly and non hazardous, and it can be applied easily in a washing machine.