Hi there, Bexico, welcome to the forum! Congrats on making the first step. The road ahead's a long and arduous one, but there will be plenty of wonderful people to help you along the way.

Corny dialogue over, there are a couple of different routes you can take in order to start things off. It really depends on whether you're able and/or willing to pay for treatment privately or not — if you decide to, there are a number of private clinics you can check yourself into (Dr. Curtis' Transhealth and Dr Lorimer's GenderCare being the two most prominent in the London zone) which should help get you started. As far as I know, you don't need a referral — just ring up and book a consultation, but it's quite pricey.
If you decide to go the NHS route, you'll first need to go and speak to your GP (or one that you trust) and tell them you're having questions about your gender. This will then probably lead to a conversation about what it is, exactly, that you're feeling and what you want to happen. The GP should then write to a general psychiatrist who will make an appointment to discuss your situation further, which will mostly involve some routine questions to check your physical and mental health history, but they'll also ask you about your gender and stuff like that. After that's out of the way, they should then write to your nearest NHS gender clinic (which I would imagine is London Charing Cross, but it depends where you live). They will then send you an appointment through the post, but they tend to be quite busy, so this can take a few weeks or even months. The waiting list can be quite startling, so expect your appointment to be several months away! It's worth waiting it out, though — I was offered an appointment in November 2010 (which was seven months from when I received the letter) but they had some cancellations and I was then offered one in July instead, which was quite amazing!

The prospect of waiting such a long time for anything to begin happening is quite a scary thought, so my recommendation would be to try and find yourself a nice counsellor to chat to in the in-between period while you wait for your NHS consultation. Your GP can make a referral for you to speak to an NHS counsellor, or if you have the money, you can find a gender specialist to speak to. I was terrified of having counselling at first, but I'm so, so glad I chose to do it. I found it so helpful and the guy I spoke to (James Caspian, I cannot recommend him enough) was fantastic. It can be a great way to find out about what future options are available to you in terms of transition and help you to figure out what, exactly, you want out of it. Every trans person is different of course, and not everyone has hormones or surgery! It may help you to feel a little more confident when you walk into Charing Cross (or wherever) with more of an idea of what you want. In addition to that, the NHS may require you to have a minimum of 3 months counselling before they begin to talk about hormones and surgery (if that is in your future plans of course), so it kind of kills two birds with one stone and gets it out the way early ;]
I would also suggest hitting up any local FTM groups that are going on. FTM London is one of them, you may have heard of it — it's a great group that meets on the first Saturday of every month in Camden. It's a great place to go and meet people from all stages of transition and just make some new friends. :]
I apologise for rambling inanely, I do hope this post has been at least somewhat helpful. I tend to go off on a tangent a bit and not make very much sense, so I hope I've not come across too overwhelmingly stupid! I'm by no means the most experienced person here, most of this is lifted from what I personally went through. There are a lot of different ways of doing it, and like I said everyone is different.
Very best of luck to you sir, if you have any more questions about the NHS pathway or just fancy a chat with another London local feel free to hit me up!