Referal through your doctor is the commonest way but i believe the waiting list is a few miles long so your best bet is to go private (fair warning, its pricey). Some employers/unis etc. offer it though so its worth checking with your uni (if youre a student) or employer to see if they offer it. I got some free sessions a while ago through my work but the long term and more specialised stuff youll generally need a doctors referral or pay through the nose for.