It's worth keeping Greenwich Mean Time as the time used in Greenwich, London and Britain. When arranging meetings etc, it's sometimes confusing to people far away from Britain that, during the summer, it's not "GMT" in London. That would be worse if Britain decided to use GMT+1 permanently.

What other countries do leads on from that, otherwise there's not much point to timezones.

No, it’s worth dropping the anglocentric “GMT” altogether and using UTC everywhere instead. Let’s decouple time measurement from accidents of history, and make rational choices about what we want our life to be in the future, rather than being shackled by pointless traditions.

Oh, man, gotta let our British friends hold on to something of empire. ;->