The links that follow provide information on all the organisations and people: Including their complaints services; how to identify who a person is and their contact points, e.g your local MP, the UK Gambling Commission, etc.
It is important to note that all these regulators will not deal with all the modern online bookmakers if you are based in the UK. Bookmakers wherever they are based in the world must be licensed by the UK Gambling Commission if they deal with UK customers (punters), but, as an example, this does not apply to the Information Commissioner’s Office, i.e. if a bookmaker is based in Malta for data abuses they would be regulated by the appropriate organisation in Malta. It is, therefore always best to check before wasting your time complaining to the wrong regulator.