Greg
If I were you, I would keep an eye on the news this week. On Wednesday the supreme court will announce whether it agrees with the Office of Fair Trading that unauthorised overdraft fees are subject to laws on unfair contracts.
Although some of your fees may relate to authorised overdraft facilities, there may be a knock-on effect, if the court rules in the OFT's favour.
This is todays Independent article on this subject. http://www.independent.co.uk/news/uk/home-news/customers-in-line-for-bank-charge-windfall-worth-billions-1825924.html
If your complaint only relates to authorised overdraft charges, you should follow the official complaint procedure of the building society and ask for a review of charges. If you believe that they are unfair and cannot resolve with the society, the FOS may be able to look into. I understand that neither the FOS or FSA are taking on complaints re unauthorised overdraft charges while court proceedings are in progress. This is the FOS page on this http://www.financial-ombudsman.org.uk/faq/bank-charges.html
Huckster