Although Belkin have pledged to replace my router again (which will result in me getting router number 4!), I have decided to try to get a refund from my supplier - dabs.com - as I have no confidence that another replacement will work any better than what I have been given already. However, Dabs are pulling the legal angle, saying that they have no obligation to provide a refund as it is more than 28 days since I took initial delivery (I got the initial router on 11th or 12th December).
I've explained to Dabs that I've spent the whole of this time trying unsuccessfully to resolve the problem with the manufacturer (Belkin). I'm now awaiting Dabs' further response.