Did the bike have disc brakes? I guess not!I fitted one to friends bike today.
Looks like you are running a single pannier.This one also fits:
ALLOY BIKE Bicycle Cycle DISC BRAKE REAR PANNIER RACK ADJUSTABLE FOR 24-28" | eBay
Its got so many bits that adjust that it took a few hours to fit, but made it in the end.
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It also has the benefit of improving weight distribution when you use your stand, assuming it's a side mounted one.Looks like you are running a single pannier.
A safety tip is to mount it on the 'off' or right hand side of the bike - it gives you more width and road presence in traffic.