The HMRC website states "allowable expenditure, it must be 'wholly and exclusively' for carrying on and earning the profits of your business. This means that your sole purpose for the expenditure must be a business purpose" Details of allowable expenses are available at www.hmrc.gov.uk/incometax/relief-self-emp.htm (for self-employed).
Although Liz is right about the cost for the business, you are attending these to GAIN more buiness so they are allowable. When doing the accounts for my business i put them through as networking fees (for the annual charges) and networking costs (for the money you spent of those which dont charge membership)
As for classifying them when you do SA or returns I would probably put them as 'adminisative costs' or Box 18 on the SA103s.
Gary - How are you getting on with the BNI? I think it was you that posted on here that you were hopefully going to join one? If so have you got anything out of it yet?
BNI is good! it helps being in the 6th biggest chapter in the UK, we hit 50 members last week!
It really is a different kind of networking, very structured but it works. I have probably made my £654 sign up fee back already and I've only been in since April! It has also helped me double my client base in 3 months (ok it was only 10ish when i started) and helped connect me with a lot more businesses too!
I also found out last week that im one of two BNI Bookkeepers in the whole of Norfolk! so I'm going to start venturing to other chapters and see if i can pick up even more! :D