BAAPS registrations are usually only for surgeons who have done their medical school training outside the UK,surgeons need to complete exams and jump through alot of hoops to be able to work in the UK.
I think that your main concern is that this surgeon is registered with the GMC.
Information from the GMC website.
List of Registered Medical Practitioner
Doctor Details
Results of search on: 19 Jan 2012 at 08:41:13. The details shown are valid at the date and time of the search only.
GMC Reference Number
6044865
Given Names
Stefan
Surname
Gonschior
Gender
Man
Status
Registered with a licence to practise; this doctor is on the Specialist Register
More Details
Primary Medical Qualification
State Exam Med 1991 Universitat der Gesamthochschule Essen
Full Registration Date
18 Apr 2002
Specialist Register entry date
Oral and maxillo-facial surgery From 27 Aug 2002
Hope this helps you are in safe hands do not worry,xxx