Take a look at the {http://www.independentmidwives.org.uk\Independent Midwives Association} website.
I would definitely recommend having an independent midwife. I only arranged one very late into my last pregnancy, as we were moving house and I thought it would give me the best chance of having a home birth, wherever I was when I went into labour!
Other advantages for me were:
having someone at the labour who really knew what I wanted, rather than having to write a birth plan that wouldn't necessarily be read or followed
having someone who really wanted to hear or see how I was at each appointment and took time with me, rather than ticking me off the list and having to rush on to the next woman
loads of postnatal support, especially with breastfeeding
a confidence that even if something went wrong during labour they were experienced enough to deal with it and not suggest unnecessary interventions because they were scared or just following hospital imposed policy
These are just off the top of my head. It was well worth the money and if we have number 3 I shall be booking with independent midwives again. Was about to start a rant about the NHS not offering what women (or midwives) want but shall cut it short and go for a nap with ds instead!