Our Interest Only fixed Rate ended a while back, and due to the low Bank of England Rate at the moment, we've haven't had to pay a lot of interest. Like everyone else,I know that rates may rise at some time, and was wondering whether to fix again/offset whatever, but was a bit 
when I looked at some of the Arrangement fees etc
When I (finally!) got round to reading the small print for our current Mortgage,(Woolich) it dawned on me that we could just overpay whenever we want, and get the capital down that way - no penalties, no extra fees!
SO, the basic Interest will be paid by Standing Order as usual, and I will try (hard!) to go into the Bank, and put as much as possible in when we can (easy counter transaction). If we can reduce the amount owed NOW, when Interest rates are low, it will be more manageable if/when rates go up. I realise this won't suit everyone, but mine and DH's jobs are a bit feast or famine, so it will make quite a difference in the long term to us.
I expect most people may know this, or their Mortgage may not allow it, but I was quite pleased with myself for noticing it! 