Hey Becky,
I'm not sure how up to date this information is, but there used to be an NHS Speech Therapist called Carol Woods who was based at the Speech therapy Department of Fairfield Hospital in Bury.
I went to see her for a few sessions back in 2000-2001 and it was very helpful. She has a lot of experience of working with trans people and at one time she did do some group sessions for trans support groups in the North West.
There are a lot of internet resources available to help you with feminising your voice, but it is definately useful to have a few sessions with an experienced speech therapist.
Quick tip - work on the resonance and voice projection rather than pitch cos thats much more important!
Good luck!
ps La glitch is absolutely correct when she says it's all about practice and the voice being a muscle. I had an occasion about two years ago when I found details of an old works related pension account that I had forgotten about. I know from experience about the hassle of having to write to pension companies etc to tell them about transition. And as I only wanted to know the balance on the account and had all the security details, I thought I'd phone them up using my old voice - basically impersonating the old me
However - I couldn't do it! I went on the phone using what I thought was my old voice and the guy at the pension company still called me Miss and Ma'am....and told me I'd need to get my husband to call! Anyway, I waited a couple of days and then phoned back and really had to ham it up to get a believable male voice on the phone!