Liona,
is your birth mother still living or deceased? If she is still living then you will have a problem, otherwise you have the right to see the adoption records (assuming the adoption was official and the records were not lost/destroyed) as the child of a deceased adopted person.
I have been down this route for my daughter-in-law, who's mother was adopted and died when she was very young and the outcome was both amazing and unexpected (for us and the birth family). Please PM me if you would like help with the processes involved.
Also do you happen to know her birth date and place of birth? If so, you could do a GRO search for children born with the same first and second names in that quarter, although of course there is no guarantee that her original names were retained; that did work for us though.
