It's the most famous clock in Britain – and arguably the world. 

So when Big Ben goes silent and the clock faces darken on Saturday night as part of the UK's switch from British Summer Time (BST) to Greenwich Mean Time (GMT), there may be some concern among observant Londoners that a genuine icon is broken. 

However, the clock will have been stopped intentionally (and briefly) to adjust for the time change – one of only two occasions each year when it is allowed to pause.

The change takes place at 2:00 am (0100 GMT) on Sunday, when clocks across the UK are turned back one hour to 1:00 am.

Most European countries also revert to standard time ("winter time") Sunday, although there have been calls to scrap seasonal clock changes in recent years, most recently from Spain's leader Pedro Sanchez on Monday. 

"We come up here and stop the Great Clock – we really stop it," said Ian Westworth, 63, who has worked in the Palace of Westminster's clock department for over 20 years.

Officially called The Great Clock of Westminster, it and the whole building are widely known as Big Ben – the name of the largest of the four bells in the Elizabeth Tower, which looms picturesquely over the UK capital and its parliament. 

The Big Ben nickname is thought to derive from Benjamin Hall who oversaw the bell's installation.

The well-oiled process of turning the clock back begins around 6:00 pm Saturday, Westworth said. It includes silencing the chimes and switching off the dial lights to avoid passers-by seeing the clock showing an incorrect time.

With the clock paused, the four-person team carries out a full maintenance check, which this year includes tracking down the source of an audible squeak that occurs around the quarter to the hour mark.

"We'll take it apart, service it, put it back together again," Westworth said.

Once that's done the clock is set to the "new midnight".

"We don't switch the lights on and we don't have the bells on, but we get the clock ticking and then we've got from 12 o'clock till 2:00 am to get the time right," Westworth said.

Life-changing lift

At 2:00 am the clock's lights and bells will be switched back on.

"The Monday morning after the time change, we get a lot of emails saying, you know, your clock doesn't work, you know, or I missed my train because of you," he added.

The clock itself is checked and wound up three times a week. The minute hands are made of copper sheet while the hour hands  are made of gun metal.

Getting to the clock means wearing a noise-cancelling helmet and until recently used to entail climbing 334 steps to the top of the clock-tower, which stands 96 meters high.

But after major renovation work was completed at the end of 2022, a service elevator was added.

"It changed our life," said Westworth, whose team looks after 2,000 clocks on the parliamentary estate, including around 400 which require winding up once a week.

"Back then, if we happened to forget a tool, we had to go all the way down and back up again. It was tough."

Aside from the lift and new LED lighting to illuminate Big Ben, the clock which dates back to 1859 remains largely the same – although the tools are updating. 

Before the recent renovation, his team used mobile phones to check the accuracy of the time. Now, the clock is calibrated by GPS via the National Physical Laboratory.

Despite the pace of 21st-century technology, Westworth is confident Big Ben's future is secure.

"As long as there is a good team of people behind it, we can keep this clock going for another 160 years," he said.