The competition watchdog said in March that it had granted permission for British Gas Trading (BGT) - a subsidiary of Centrica (LSE: CNA.L - news ) , the UK's biggest energy supplier - and Northern Powergrid to appeal against Ofgem's price control decision.
Take context from the input text and decide on the accurate relationship between 'Centrica' and 'British Gas' from the options provided.
Options: distribution format, owner of, brand, headquarters location