Briefly I went to a posh seminar with a friend a while back. My friend had a word afterwards and the company concerned wanted something like £2000 to do a codicil - it simply handed the work over to a lage firm of City of London solicitors. My friend's solicitor did it for £50. I think a straightforward solicitor is the way to go and one needs to shop around making sure one finds a solicitor geared up for this sort of business. The LAW SOCIETY maintain lists.
Regards, Fedora.