Probably 10-15 years ago, maybe? I can't remember exactly. Not more than that, I'm sure.
Sure sounds like a COCOT if it was that time frame, as they proliferated during the 1990s.
The British A/B coinbox pictured above is from a very different era. The first of these were installed in the mid 1920s, and they became the standard G.P.O. payphone until the very end of the 1950s.
The beginning of STD (Subscriber Trunk Dialing, i.e. customer-dialed long-distance) and the desire to have payphones handle such calls without operator assistance led to the introduction of a new type of coinphone in 1959, and these post-pay units gradually replaced most of the old pre-payment boxes during the 1960s:

This one had no buttons. You just picked up and dialed, then when the called party answered you'd hear
pay tone, which was the signal to insert your money to allow the conversation to proceed. Once money had been deposited there was no way to get it back.
This is all somewhat relevant to the subject of how people
used to answer the phone in Britain, because if you answered a call and heard that tone (known colloquially as "the pips") you knew the call was coming from a coinphone and that you'd have to wait for the caller to insert his money before you could talk to him.
A few of the old A/B coinphones survived into the 1970s (all payphones had to be converted in 1971 for the new decimal currency), but they were relatively rare by then. The very last A/B phone was in a remote part of the Scottish Highlands and was finally withdrawn from service around 1983/84. Ironically, at that time the newly created BT has just started to introduce new phones to replace the 1960s/70s units, which were again pre-pay, only this time microprocessor controlled. These early 1980s payphones are the oldest still in service.
And all of that is probably far more U.K. payphone history than anybody here ever wanted to know, but it's all part of the tapestry of how people's use of the phone has changed over time.....
