use the internet to search for culinary schools, food enthusiast programs, night courses, Saturday courses etc.
Here in the US, cooking classes may be offered through a culinary school or college or university. Many are offered at Arts Institutes and technical schools. So search a wide variety of options. London is bound to offer many opportunities.
Another option is to hire a private chef to instruct you or you and some like minded souls in certain skills, methods, recipes, etc.