British citizenship

[paddym1]

I was born in India in 1941 to British parents - my father was British soldier posted to India prior to WW2, my British-born mother and my siblings accompanied him as was British Army practice at the time. I have a British Birth Certificate giving father's Regiment, Regimental Number and Rank, place of birth. Assuming my Birth Certificate and both parents' Birth Certificates (both born in Wales to British parents) are in order, under what UK Act or Regulation am I a British Citizen, or entitled to claim such? I made enquiries to the UK Govt, but received only a documentvwith dizens if links, none of which appear relevant to me. Thanks for any guidance.