Thanks for all the advice everyone, some very useful stuff here.

Unfortunately, I won't be doing anything for a while. The tax office made a mistake on my tax code - someone stuck an extra zero on the income from some part time work I did last year! As a result my February pension was substantially down. I have sorted out the immediate problem but it has left a hole in my finances for the time being. It should get sorted eventually, but not anytime soon, I suspect.

Meantime, I have the thread on the tracer so I can look back at it when I need to.