Clocks go back: what darker evenings do to your body clock and the roads

At 2am on Sunday 25 October the clocks will go back one hour across the United Kingdom, British Summer Time will end and the country will return to Greenwich Mean Time. The headline is an extra hour in bed. The part nobody puts in the diary is what follows: weeks of leaving work in the dark, a body clock that argues with the alarm, and a measurable rise in collisions on roads that suddenly feel unfamiliar.

None of it is dramatic, and none of it is unavoidable. But the first fortnight after the change is the window where a little planning pays off most — for drivers, for parents collecting children, and for anyone who already finds the back end of the year heavy going.

What actually changes on Sunday morning

Clocks move from 2am to 1am, so the night will be 25 hours long. Phones, laptops and most smart devices handle it without being asked; oven clocks, car dashboards, central heating programmers and some older watches do not. Sunrise will arrive an hour earlier by the clock, which is pleasant if you start early, and sunset will land an hour earlier too, which is the half of the deal that causes the trouble. By late November, much of England sees the light go before 4pm, and Scotland earlier still.

The two dates are fixed by rule rather than by weather: British Summer Time runs from the last Sunday in March to the last Sunday in October, as the Royal Observatory Greenwich sets out. There is no option to opt out of it locally.

The collision spike that comes with the dark

This is the part of the clock change that is genuinely worth knowing. Analysis for the RAC Foundation found that the fortnight after British Summer Time ends carries, on average, 278 more collisions than the fortnight before — a rise of around 5.1%. For collisions involving pedestrian casualties the gap is sharper: roughly 102 extra collisions, up about 11.3%.

The reason is mundane. The evening peak, when traffic is heaviest and children and older pedestrians are still out, shifts from daylight into darkness overnight, while habits take weeks to follow. The Royal Society for the Prevention of Accidents argues that a different clock arrangement would spare around 450 deaths and serious injuries a year on British roads — a campaigning estimate rather than government policy, but one built on the same seasonal pattern.

Practical steps for the fortnight ahead:

• Clean the inside of the windscreen as well as the outside — interior film scatters oncoming headlights badly.
• Check that every light works: headlights, sidelights, indicators, brake lights, fog lights and the number plate lamp.
• Leave more room than feels necessary around cyclists and on unlit lanes, where speed is far harder to judge.
• If children walk home, do the new route with them once in the dark before they do it alone, and add something reflective to the bag rather than the coat.

Why your body takes a few days to catch up

An hour sounds trivial, and for most people it is. The internal clock, though, is set largely by morning light, so it drifts rather than jumps. Expect a few days of waking earlier than you meant to and flagging mid-evening. Sleep specialists broadly agree on the unglamorous fix: keep the same bedtime and wake time through the weekend rather than banking the extra hour, get outside in daylight early in the day, and keep screens and heavy meals away from the last hour before bed. Our look at the loops linking sleep, screens and mental health in young adults shows how quickly a disrupted week can harden into a habit.

Seasonal low mood, and where the line sits

Darker evenings also flatten the mood for a lot of people, and for some that goes further. Seasonal affective disorder is recognised by the NHS as depression with a seasonal pattern: persistent low mood, lethargy and daytime sleepiness, difficulty getting up, loss of interest in things normally enjoyed, and cravings for carbohydrates. Symptoms typically begin in autumn, are worst across December, January and February, and lift in spring. Published UK estimates vary, with NHS material commonly citing around two million people affected, and other sources putting it nearer three in every hundred.

Treatment options set out by NHS services include talking therapies such as cognitive behavioural therapy, antidepressant medication where appropriate, and light therapy — typically sitting in front of a light box for 30 to 60 minutes each morning. The distinction that matters: a dip in energy for a week after the clocks change is ordinary, while low mood that persists for weeks and gets in the way of work, study or family life is worth raising with a GP rather than waiting for March.

A short list for the week ahead

• Reset the car, the oven and the heating programmer on Saturday evening, not Monday morning.
• Check lights and tyres before the first dark commute.
• Hold your usual sleep schedule rather than lying in on the Sunday.
• Book daylight into the diary: a walk at lunchtime beats one after work, which will no longer be an option.
• Expect the heating and the lights to run longer — worth knowing how the fixed part of an energy bill works before the first winter statement arrives.
• If you have not yet checked your eligibility for this season's NHS winter vaccinations, the clock change is a useful prompt.
• Nervous pets face a noisy fortnight as well as a dark one: our guide to getting a dog or cat through Bonfire Night covers the preparation.

Frequently asked questions

Do the clocks go back at 2am or 1am?

At 2am BST, which becomes 1am GMT. The change always falls in the small hours of the last Sunday in October so that it disturbs as little of the working week as possible.

Will the UK ever stop changing the clocks?

There is no legislation in progress to end the twice-yearly change. Road safety bodies have long campaigned for lighter winter evenings, while farming and Scottish interests have long argued the other way. For now, the current arrangement stands.

Is a light box worth buying for winter low mood?

Light therapy is one of the options NHS services list for seasonal affective disorder, and some people find it helps. It is not a substitute for assessment: if symptoms are persistent or severe, speak to a GP first, particularly before combining it with other treatment.

Sources

• Royal Observatory Greenwich — when do the clocks go back
• RAC Foundation — road safety and the clock change
• NHS inform — seasonal affective disorder (SAD)

This article was written with the help of artificial intelligence. Editorial policy