You shouldn't get a failure like that from speed. Certainly not any speed that you're capable of doing on the highway in a Clio Sport.
If you haven't mistreated the tyre by bouncing it off a curb - if there's any rium damage it'd be incriminating for you, but the absence of rim damage doesn't prove you've never hit a curb with the tyre - it may be that the tyre was faulty. That there was a defect in the the construction that resulted in separation of the layers of the tyre.
Don't just assume its your fault. If you only bought them last year, 2006, go back to the dealer you bought the tyres from and demand that they look for sign of damage to the tyre wall from impact, up to and including returning the tyre to the manufacturer for their inspection, and if there isn't any to consider replacement under warranty, or at least a pro-rata replacement, ie, you refund you for the amount of tread left on the old tyre. If you can, get a close up photo of the area of damage and look for abrasions and cuts that'd indicate damage, and if there's none you may have a good case.
Of course even if there's no sign of damage they could still argue that it was the result of being run with insufficent pressure in the tyre that overheated it and causes separation of the layers of the casing.
So what's your story (if its true!)?
1. you've never underinflated the tyre,
2. you've never bounced it off a curb,
3, it became evident after a run at speed, but reasonably legal speeds,
4. its not a user-caused fault so it must be a construction fault, so you demand a replacement tyre.