Merlin infiltrates Mordred's lair in the nether world to find out what he's plotting. On being discovered he manages to escape to the Earth's surface but leaves his staff behind. Some while later when he persuades King Arthur to jump into a lake to retrieve Excalibur from the Nether World he has his staff back.
In the early scene when the knights attack the big rig tanker truck, the front of the truck displays a yellow, non-British number plate (license plate). The next time it is seen - seconds later - it has a British plate. The truck is also not a type seen on British roads.
How do the two children climb into the boot of Maxwell's car as when she comes out of the house she presses her key fob to release the locks.
Guinevere wears chain mail, but has a very revealing neckline, which somewhat defeats the purpose.
How do the kids get out of the cat boot in the high security car park after being locked in then evade the security systems to get into the plant then find their way through the ducting system where they're next seen. It appears a large cut was made here.
When Merlin falls down it is clear that his underwear is more "Marks & Sparks" rather than what would be expected in AD500.
Stonehenge is located on Salisbury Plain, which is flat, open ground, not dense woodland as depicted in this movie.
For many, many years now, StoneHenge and the "immediate" surrounding area; with its National Trust paths, fences and barriers has looked completely different to how it is portrayed in the film. Even if Stonehenge had been magically repaired for the event. The stones are all in the wrong places! Not to mention the strange invisibility of the 3 roads which run right past it.
Kate says to Guinevere 'A penny for them' (her thoughts) and she knows what is meant which is strange as she knows nothing of the present.