OK.... well I'm not clinical or indeed a mother so take any advice I give with a pinch of salt.
Firstly I would say is there any way his behaviours are learnt? (Do you do any of these without thinking when you're anxious?) Is it possible he's picking up on stress or worry in home? Is it possible that this is his way of getting undivided attention? (NOT the same as being attention seeking) And is there any way he's picking up on your anxieties about him? Any of these things can cause children to be anxious. Am sure you know all that already in any case with your teaching background, (it's just worth bearing in mind).
Being a bit funny about dirt or wanting a blanket just so is not necessarily so bad, might just be a comfort thing and I guess it has to go in to context of how he behaves in general, (I was (and still am) horrified at dirt on me and I carried a blanket around with me to about age of 9 for comfort).
I've just checked and there should be a CAMHS (child and adolescent mental health service) in your borough (actually I think every borough has one but some are more difficult to find info on than others!) Now just about every CAMHS I'm aware of has some variation on how you can refer to them but I believe that GP's are able to make referrals so it may be worth speaking with GP. Is there a way you can discuss on the phone prior to making an appointment with them to get their take on what the best way forwards is? I'm more thinking about not adding to his anxiety by taking him to GP if GP can tell you on the phone that they can't refer to CAMHS (am pretty sure they should be able to though).
I'm not too sure of online forums or places for children to go to get further information but I imagine a CAMHS team would definitely know. I did find this leaflet online which I think is interesting, well the bit about school age children, so perhaps you will find some parts helpful too
http://www.mentalhealth.org.uk/content/assets/PDF/publications/anxious_child.pdf
Anyway, not sure if any of this even remotely helpful as it's not exactly my specialist area but hopefully something in my answer might give you an avenue to search.