The clock over the old Corn Exchange in Bristol has two minute hands. The red minute hand shows Greenwich Mean Time and the black minute hand shows Bristol time!
It is a throwback to a proper revolution in measuring time, following the development of railways and telegraph communications.
Before the railroads came, there was no particular reason why people in Bristol should keep the same time as people in London. Not just Bristol, in other parts of the UK and the world, time meant local solar time.
Natural or solar time time depends on a location's position in relation to the Sun. Natural noon or midday in a place is when the Sun is at its highest point above that location.
After the expansion of railway networks, running trains accurately required standardization. It was not just trains. Read the full story of that significant change here.
Bristol is at 2º 35' (West) of Greenwich, so a bit behind London in terms of Sun's apparent daily journey. Before the introduction of standard time zones, when it was noon in Bristol it was already 10 minutes past noon (twelve) in London.
The Bristol clock above the Corn Exchange is still showing the historic solar time difference to London.
Greenwich Mean Time (GMT) became, by law, UK's Standard Time zone in 1880. British Summer Time (BST) was adopted in 1916, and clocks started being switched yearly to BST, which is GMT+1. At the end of the BST period, it is back to GMT.