All dog food is 20% off in B&Q at the moment.
I focussed on Wagg Worker because it's outstanding value due to it's Tax free status.
Dog food is generally stocked only in the large B&Q warehouse stores.
Buy it on a Wednesday with a Diamond Card & 60+ friend/relative tagging along and you get a further 10% off making it £7.11!
Supermarkets ordinarily charge ~£9.90 for this.