Focus DIY - Discounts & Voucher Codes

On turning 60 I was delighted that I could claim a 10% discount card from Focus and even more delighted by the frequent mailings I get sending me 15% dicounts valid for a short period.
I have made use of them regularly over the past few years and saved a lot of money on items I would have bought at the regular price.
When I needed to replacemy lawnmower naturally this was oneof the first places I went to.
Whilst it told me on the back of my latest 15% discount card that I could not get a discount on lawnmowers no such statement was included on my regular 10% card.
Imagine my embarrasment when I arrived at the checkout to be told that my discount could not be used against the price of the lawnmower.
Perhaps if the young man who was serving me had been more friendly I wouldn't have stalked out of the shop leaving him to replace the lawnmower that I had carried to the checkout and vowing never to shop at Focus again.
The actual get out wording on the backof the card says,"This card cannot be used in conjunction with any other discount card or money off voucher or major discount promotion as specified. "
I don't know where it specifies when it can and cannot be used