The UK uses Greenwich Mean Time (GMT) as its time system. The whole country uses the same system.
We are one hour behind Paris and five hours ahead of New York.
It’s worth taking a trip to Greenwich by train, bus or DLR, to see the observatory and the meridian and the beautiful parks and buildings. Note that there are big hills to climb and it’s often very busy.
At the end of March the clocks go forward one hour and we use British Summer Time (BST). We are synchronised with Europe but not with the USA, which can go onto daylight saving some weeks earlier.
At the height of the summer it is daylight by 5am and more-or-less still light at 10pm, so you can come out of the theatre and it is still daytime.
Clocks go backwards at the end of October. Again, the USA is different. In the depts of winter it is still dark after 7am and dark again by 4pm.