I know a great Cranial Osteopath, but they are in Knightsbridge....a bit of a treck, but they are worth it. If your interested, let me know and I can send along details.
Otherwise, its worth checking out Neals Yard Remedies's Therapy Rooms in Borough Market.
Their practioners are generally really good and I know they have at least one (the Borough Market branch is small) on their books.
Their website is www.nealsyeardremedies.co.uk
Neals Yard Osteopath does a mixture of cranial and other. There is a soceity of cranial Osteopaths. If you google it who can give you a list. Other that that phone or pop in to The British School of Osteo at Borough, Sawyer St. They may have some numbers.