1ST File a complaint with BA @
https://www.britishairways.com/trave...m/public/en_ca
2nd File a complaint with the UK regulator of the Airline @
https://www.caa.co.uk/Passengers/Res...-compensation/
Bad News: The Airline is not responsible for items stolen by other passengers. Unless you can show how they are at fault or one of the Airlines Employees is at fault you wont get anywhere with your complaint.