Over an hour at the dentist today (even if she is very lovely), left me feeling unable to bother any more about searching the interweb. So I went back to Halfords and got the only one that suited. Yuasa HSB053, 48AH and 430A (CCA), with a 5 year warrantee. Normally £75 but as someone here mentioned price match, I had a look and the lovely people at thebatteryshop.co.uk had it up for £49. Bless 'em. I think Halfords should have added the delivery cost of £8, but didn't, so I left sort of smiling. In a lop sided, drooley sort of way.
In case anyone else, like I was, comes looking for the battery size etc. Details are: Yuasa HSB053, 48AH and 430A (CCA) but most important the size is 238x129x227mm.
Hopefully it'll last longer than the useless Honda battery did.