Wow, thanks for the replies.
There have been some very interesting points raised. It still sounds like a PhD could very well be for me and it's nice to hear that 30 isn't too old.
I studied pharmacy in Cardiff, and ideally I would like to do my PhD there too. The points about having a decent supervisor are familiar to me, but I guess it is hard to know until you are actually working for them.
I'm thinking that I should strike whilst the iron is hot as I have made some good connections in the university that should hopefully help with references etc.
On a separate tangent, I know that a PhD will take up a lot of hours in the week, but do you find that you have more control over what hours you work than say a 9 - 5 type job. I have no problem working late in the night / weekends if it means that I could pop out for a ride more easily during the day etc.
I'm glad that overall, the replies seem broadly positive.