What do the British say for 'Happy Birthday'?

Answer 1

Happy is clapping the hands and smiling (showing happiness) Birthday is generally signed as

holding both hands in front of you trouser pocket area with the fingers pointer in down and palms facing your pockets. Move the had up in front of you as though presenting somthing - the hand then face upward and fingers pointing the person you talking to

Baasics of the signs Happyfollowed by baby comes from (birth) gesture. Happy Birth(day)

Answer 2

Exactly the same - Happy Birthday.