The solicitors who did it for you will have it. You also don't actually need it. If someone asks for it say you are using the new name under 'right and useage'. As long as you do not answer to any other name you can use what you want without having any official documentation.
Thanks, I did obviously ask the solicitor but their records do not go back so far. The passport office are not normally very open to anything which does not conform to the words on their forms. They require a birth certificate which has another name in this case! Thanks anyway, he will see.