'Minder' Episode in Series 7 - GOOF.

When 'Mrs Cameron' is making a Call from a (1992 UK)Public Phone Box, The Phone Box Machine's Screen clearly shows that there is Zero Credit for the length of time that she was speaking. The conversation could not have happened for that length of time before the 'Buy more Credit' noises would have been beeping and an advisory notice on the Screen would have been flashing to put more money in the Coin Slot. If it was ignored then the Caller would have been cut off.