Do i have to join a club to be affiliated?

Its the only way Jon! thats what afilliated means

You'll just have to become afflicted and hope that's close enough.

To be affliated to UK athletics you have to be a member of a club. Details here:-

http://www.englandathletics.org/page.asp?section=725&sectionTitle=Registration

Being a member of a club does not mean you have to turn up every week. Some people are club members and only see other members at races.

However, there are other finacial benefits to being a club member and that is a 5% - 15% discounts at some running shops. Also members tend to car share or book minbuses / coaches for some events. Joining a club will only cost you about £10 per year plus your England athletics fee which some clubs subsidise.

Here

Jon - you say you have zero interest in joining a running club  you will be surprised how much they help you progress, not only that, you meet like minded people and of course get races cheaper  give it a go

If you really don't want to join a club then there are some internet based ones that you might prefer.

But I also aggree that joining a club is a good idea.  They are not as cliquey and fixated on racing as most people think.  Lots of clubs are for people of all abilities and all interests from serious club runners to people that prefer the social side while doing a bit of exercise.  And as others have said, you don't have to turn up to club sessions.