Sammy Jenkins
BBC News, Live page reporter

The A303 has been closed in both directions near Stonehenge due to a high volume of vehicles parked on the side of the road and pedestrians on the carriageway.

Wiltshire Police said the road is closed between the A360 at Longbarrow Roundabout and Countess Roundabout, Amesbury.

"The closure will be kept under review," it said.

Motorists are being told to use an alternative route via Countess Road and through Larkhill.

"We would like to remind motorists to drive safely and cautiously due to the increased risk of pedestrians walking in the road," it added.

To answer this, let’s look at the two ways the start and end of seasons are defined.

One is the astronomical seasons, which are based on the position of the Earth in relation to the Sun. The astronomical summer is often marked as beginning on the summer solstice.

The Met Office says this year, astronomers are marking summer as starting today and ending on 22 September - but the dates shift slightly each year.

Meteorological seasons are another way of defining the start and end of seasons. They’re based on the annual temperature cycle and are split into four quarters made up of three months each - a more consistent way that makes it easier to compare seasonal statistics.

This means meteorologists always class the northern hemisphere’s summer as being from 1 June to 31 August.

So, is today the start of summer? It depends on whether you’re asking an astronomer or a meteorologist.

Good morning, and if you're up in the middle of the night joining us, thank you, you have a very long day ahead - literally.

Today marks the summer solstice, the longest day and shortest night of the year, and as you read this thousands of people will be gathering at sites around the UK to mark the start of the astronomical summer.

We're up nice and early (or very late, dependent on your view point) for you, with reporters at Stonehenge, the Avebury Stone Circle and Glastonbury Tor.

There's a good chance if you are reading this in the middle of the night you're struggling to sleep in the heat - and it's expected to continue today, with temperatures of up to 34C and a yellow warning for thunderstorms.