The English curry house is a place where you can get Westernised versions of Indian dishes as well as Indian style dishes (e.g. balti). In general, the chef will have prepared large quantities of curry sauce in advance and will add this, along with other ingredients in varying quantities. In a typical UK Curry House, there will, therefore, be no fundamental difference between Madras, Vindaloo and Phall dishes, except for the Scoville rating.
The value of curry houses in extending one's culinary experience is somewhat limited. There are notable exceptions to this (e.g. Veeraswamy, Chutney Mary's) and some say there is a tendency for curry houses to be returning to more traditional methods.