Instructions:1 To qualify for a 20% discount, all purchases must be made in a single transaction and in person at any Homebase Store. The 20% discount will be deducted when the voucher is presented to the Homebase cashier at the time of making payment. Only the original voucher will be accepted.
2 This 20% discount is not valid against purchases made on homebase.co.uk, over the telephone, on national 10% and 15% discount days or preview evenings, or in connection with concessions within any Homebase store. This discount cannot be used on any Store Managers locally price reduced items, the Homebase Trade Card or against Hire Station items.
3 This voucher cannot be used against delivery charges or purchases of gift vouchers, installation and assembly services. Only one voucher can be used per purchase and it cannot be used in conjunction with any other promotional voucher or coupon or with the Homebase or Argos Staff Discount Card.
4 This voucher remains the property of Homebase Limited and is valid for a single use only [...]
There are some more terms in the small print on the voucher.
Just take this voucher to B&Q and get a further 10% off re price match.