Which cities in Britain have subways?

In Britain, only London has a subway. London's subway has 1 1 lines. As long as you enter the subway station, you can see the subway route map everywhere, and it is easy to get it for free. In addition, there are many service information desks in the subway station. Just tell them where you want to go, and they will enthusiastically tell you which subway line to take and where to transfer.