LSR, which is where it will probably be repaired, are reputable; they're not a bad bet at all if you need a paid for repair on older kit. I think they used to have something to do with Karrimor before Sports Direct destroyed it. In a way it will be good for you because it will mean it comes back with the defect you've found fixed but no other defects as you risk if they swapped it.
Out of interest, can you elaborate? Sports Direct destroyed what?
This may or may not be relevant to a different question I was thinking of asking when I saw this thread.... What would people's opinions be of this situation, which is not too dissimilar from the OP's question...?
About 6-7 months ago I bought a large Karrimor rucksack from Sports Direct for about £35 - the kind of one that looks like it probably should be a lot more expensive, but Sports Direct pricing... A week or so ago one of the straps tore off as I was putting the rucksack on, so the rucksack is now useless (Luckily I was putting the rucksack on for the very last few minutes on a trip, of walking to the station to my house). Now I know I bought the rucksack some time ago, but of course you don't use rucksacks every day. If memory serves me correctly, I've probably taken it on 3 trips (by rail) where I was going away to see friends etc. for a few days. So I've probably worn it for maybe 5-6 hours at most in total (with the rucksack maybe spending another 10 hours or so sitting in train carriages etc. full of stuff). Other than the broken strap, the rucksack still looks to my eyes clean and very close to new. My inclination was to write to Sports Direct, explaining the situation and requesting an exchange for an equivalent new rucksack (I haven't yet done that).
Bearing in mind the discussion in this thread, what are people's opinions on (a) what morally I ought to feel entitled to, and (b) what my legal rights would be, if it did come down to having to push them.