I am a British citizen living in France since 2006. My daughter was born in France (her father is French). Before applying for a British passport for her I need to know whether I qualify as a British citizen 'otherwise than by descent'. The reason for asking is that I was born in Tanzania in 1969. My parents were married, both British and born in Britain. My father had a contract with Britain's Overseas Development Agency to teach in a secondary school in Dodoma. If this counts as 'crown service or similar', does this mean I can pass British citizenship to my daughter?
You are British, but do not know if you can transmit your nationality to your daughter because you may (or may not) be 'British by Descent', it's the type of British that cannot transmit their nationality. The only people allowed to transmit British nationality are 'British Otherwise than by Descent' (i.e., born in the UK to settled parents, etc etc).
The question of your nationality hinges upon whether or not the Overseas Development Agency was considered Crown Service in 1969. If so, your daughter's British citizenship has already been transmitted and you should go ahead and register her. If not, you should investigate if your daughter can qualify under one of the precedent-based scenarios.
The answer to your question is: for either of those options, there is no definitive answer and any answer you get will not be applicable to anyone else. This is because nationality law is so fiddly-bits, and the ultimate decision relies on caseworker's determination.
There is a specialised casework unit called the Permanent Migration Directorate of UKVI. It is based in Liverpool and I highly recommend their work and their knowledge of nationality law. One of those caseworkers will have to dig back 47 years to learn your status! Sadly, the contact details of the research unit are classified (heaven knows why, I never asked, it's just a part of WHAT IS), so you will have to contact them via official channels.
Honestly, the most straight-forward way to do this is to apply on behalf of your daughter and to ask them to consider any of the precedent-based scenarios if her application does not succeed. You can find information on how to register your child on the net.
You can begin with the Nationality Checking Service (who are also pretty good but will have to make a referral in your daughter's case).