My child (now 15) has her original birth certificate, her long form birth certificate (which I believe has her former name as well), her new short form birth certificate, and her adoption certificate. I have told her from the age of 1 who her birth family are, shown her pictures, and explained in the most age-appropriate way I can why I am her mum now. She understands the differences between biological, legal and social parenting and that her birth mum will always be her biological mum.
This is considered best practice in modern UK adoption. The emphasis is on openness, honesty and helping your child to come to terms with what has happened to them. Although no one can stop an adoptive parents from lying after the final hearing, I don't believe you would be approved if this was known. Certainly, when I adopted an 11 month old, the social workers were insistent that I had to start telling her BEFORE she became verbal, so it would never come as a shock.
I think losing your birth family is always traumatic, and adoption is always a tragedy for the child. Adoptive parents have to always work with this, while also giving the child as happy and normal a childhood as possible. It takes a great deal of commitment and maturity.
Why is it different from surrogacy? Because, sadly, it is sometimes necessary. (Of course the UK is different from the US here, because we have a much higher abortion rate so nearly all adopted dc have been removed from their families rather than offered up.) Adoption is about finding next-best-thing families for children that are already here, whereas surrogacy is about deliberately creating the 'primal wound' that adopted dc also face.