It would seem, as already suggested, that you have far exceeded an acceptable time scale to take up this matter with Watford Electronics.
If you fail to realise after more than a year that something appears to be amiss - and it may not necessarily be so with either the rewriter or the CD-RW disks - then you cannot reasonably expect the retailer to become involved.
You are right to expect under the SOGA (1979) that products will be fit for their purpose and to last for a reasonable time, but to say you are stretching this beyond acceptable limits in this instance is putting it somewhat mildly.
To put it another way, if you were to go so far as to take the matter to the small claims court, I'm pretty sure that you would not only lose, but would also be meeting the defendent's costs.
As for installing a different operating system and then later purchasing a brand new computer system merely, it appears, to try and get a £40-£50 rewriter to work properly, seems to me to be stretching credulity somewhat too far.