The new Guy Ritchie film about King Arthur (King Arthur: Legend of the Sword), which opens in British cinemas this week, showcases some of Britain’s wildest landscapes, from North Wales to the Scottish Highlands. But it is unlikely to become a primer for students of Britain’s post-Roman Dark Ages. The Arthurian legend has grown a very long nose in the past 1,000 years.

If Arthur existed at all – and historians disagree on that – it was as a fifth or sixth-century warrior-king who defended Britain in a series of battles against the invading Anglo-Saxons. He was first mentioned in ninth and 10th century texts – all the stuff about Excalibur, Camelot, the holy grail and so on emerged much later in medieval embellishments of the tale by Geoffrey of Monmouth, Chrétien de Troyes and many others.

Ritchie’s Arthur (played by Charlie Hunnam) is more of a geezer than a parfait knight – the fact that David Beckham has a cameo role and that the film’s catchline is “Raised on the streets. Born to be king” should prepare you for a gangster flick with chain mail. But the tosh quotient may be lower than you think for Ritchie has chosen some intriguingly apposite locations to represent the Britain of Arthurian times.

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Filming has taken place across the country – including Windsor Great Park, where scenes for Harry Potter and the Deathly Hallows, Parts 1 and 2 were also shot, the remote Applecross peninsula in the Highlands, and the Isle of Skye – but the backdrops that really put the X in Excalibur are in North Wales.

Is this a coincidence I wonder? Or does Ritchie keep a copy of Historia Brittonum on his bedside table? For this weighty work – written in Latin in the ninth century, possibly by a Welsh monk – chronicles Arthur’s battles against the Saxons and alludes to the valley in Snowdonia where Ritchie chose to film.

Nant Gwynant is sliced from Snowdon’s south-eastern shoulder and bejewelled with lakes above and below Credit: ALAMY

That valley, called Nant Gwynant, is sliced from Snowdon’s south-eastern shoulder and bejewelled with lakes above and below. (The descent on the A498, from the Pen-y-Gwryd Hotel to Beddgelert, is one of Britain’s most scenic stretches of road.) Just past the lower lake, Dinas, a solitary hill rises like a balding skull to the right of the A498. This is Dinas Emrys and on it, according to Historia Brittonum, lived Jude Law – sorry, lived Vortigern, the character played by Law in Ritchie’s $100 million epic.

The lower lake, Dinas Credit: ALAMY

Vortigern – who has been co-opted into Arthurian legends only very recently – was, possibly, another leader of the Celtic Britons who opposed the Anglo-Saxons. His story in relation to Dinas Emrys is complicated but does include a fortress with a bad case of subsidence, a red dragon and a boy-wizard, Ambrosius, who is a forerunner and prototype of Merlin.

Filming for King Arthur: Legend of the Sword also took place a few miles north at Tryfan, a mountain to the west of Capel Curig whose resemblance to a knuckle-duster no doubt caught Ritchie’s eye. Tryfan is mentioned in another early Welsh text as the final resting place of Bedivere who also pops up in later legends as a full-blown Knight of the Round Table (he is played by Djimon Hounsou in the film).

The view from the top of Mount Snowdon

I could go on – the hills and valleys of Snowdonia, where the pulse of ancient Wales beats strongest, are alive with Arthurian echoes that conceivably have some sort of connection to historical reality. The same cannot be said for other places that are much more strongly associated with the Arthurian legend of popular imagination.

Tintagel Castle is a prime example. This ruined medieval castle teetering on the north Cornish cliffs is a major attraction at least in part because in the 12th century Geoffrey of Monmouth decided that this was where Arthur was conceived. Yet the castle didn’t exist until a century later, when Richard, Earl of Cornwall built it precisely in response to this fabrication in order to give himself a cameo in the story.

Tintagel Castle has no place in Arthurian legend Credit: VALERY EGOROV - FOTOLIA

English Heritage, which administers Tintagel Castle, has not been above milking this phoney connection – last year it was accused by a Cornish heritage group of peddling “dumbed-down populist trash” when it commissioned a sculptor to carve the face of “Merlin” into a rock on the site.

But in the end, does it matter? Ritchie is merely a Geoffrey of Monmouth de nos jours and the legend, besides being infinitely durable, has been a boon to tourism since a Cornish earl’s new-build put Tintagel on the map. Places that have muscled in on the Arthur story down the centuries tend to the mystical and atmospheric and are worthy of our attention in their own right.

Windsor Great Park, where filming for Guy Richie's epic also took place Credit: H&B PHOTOGRAPHY/Matt Gibson

10 Arthurian sites – marked out of 10 for authenticity

1. Tryfan, Wales

On south side of A5, above Lake Ogwen, in Gwynedd. Resting place of Sir Bedivere. 6/10

2. Dinas Emrys, Wales

Just north of A498 at south end of Lake Dinas, Gwynedd. Fortress of Vortigern. 6/10

3. Tintagel Castle, north Cornwall

The clifftop castle where Arthur was (not) conceived (english-heritage.org.uk). 0/10

4. Queen Camel, Somerset

One candidate for the location of Arthur’s final battle, the Battle of Camlann, in which he perished (queen-camel.co.uk). 5/10

Cadbury Castle, Somerset Credit: ALAMY

5. Cadbury Castle, Somerset

This late Bronze Age and Iron Age hill fort could be the site of Camelot. 4/10

6. Glastonbury Abbey

The abbey doesn’t promote the idea that Arthur and Guinevere lie buried here. The story comes from Geoffrey of Monmouth (glastonburyabbey.com). 1/10

Glastonbury Abbey Credit: Fulcanelli - Fotolia

7. Liddington Castle, Wiltshire

An Iron-Age hill fort and possible site of the Battle of Mount Badon in which Arthur is said to have slaughtered 960 Anglo-Saxons single-handedly. 4/10

8. King Arthur’s Round Table, Eamont Bridge, Cumbria

The name of a Neolithic henge near Penrith. Was it really Arthur’s jousting arena? Nope (english-heritage.org.uk). 0/10

9. Round Table, Winchester

The wooden table, popularly known as the Round Table, that hangs on the wall of the Great Hall was made in the late 13th-century. In the reign of Henry VIII, it was painted to show the king as Arthur, surrounded by his knights (hants.gov.uk/greathall). 0/10

10. Arthur’s Stone, Dorstone, Herefordshire

A neolithic burial chamber above the Golden Valley which isn’t the spot where Arthur slew a giant (english-heritage.org.uk). 0/10.

King Arthur: Legend of the Sword will be screened at British cinemas from May 19.

Pen-y-Gwryd Hotel, Nant Gwynant (01286 870211; pyg.co.uk); double rooms from £90 a night.