Audio problem: When Irongrond fires his first gun, the sound is heard before the gun actually fires.

Revealing: The explosion of Irongrond's castle is obviously stock footage of a quarry explosion.

Factual error: How did potatoes come to appear in a 12th century kitchen? The potato was unknown in England until Sir Walter Raleigh brought them from back from the Americas on one of his voyages in the late 16th century, at least 400 years after the period in which this story is set.

Other: After Linx plants his flag in the ground claiming Earth, Irongrond and Bloodaxe look offscreen for no reason, as though the shot is finished.

Plot hole: How did Rubeish's glasses managed to improve his chronic shortsightedness when they are obviously plain lenses?

Plot hole: How did UNIT soldiers manage to get the TARDIS through an ordinary door into the Doctor's dorm in the research centre? The Doctor's labs in the various UNIT HQs had either double doors or a removable partition wall. The research centre is supposed to be an ordinary country house with single doors and solid walls. The TARDIS is larger than the average wardrobe and, unlike most modern wardrobes, doesn't come apart so it can be got through doorways. The TARDIS is known to be a "Type 40 capsule"...but there's never been any mention of the TARDIS being an IKEA-style "flat pack self-assembly" time machine...

Plot hole: The Tyrannosaurus Rex which appears in this story does not actually roar; instead it says the WORD 'roar' several times. There may be little scientific evidence as what sound a T.Rex makes, but it is unlikely that any of them spoke fluent English...

Revealing: When Grover and Whitaker struggled over the time machine at the very end of episode six, the console wobbles and jerks as though it were very lightweight.

Continuity: In episode 2, when the Doctor and Brig arrive at the scene to stun the dinosaur, they leave the stun gun in the jeep. Mike Yates glances down at it and we can see that the sabotage disk is already attached - although he doesn't actually put it on until later.

Visible crew/equipment: In episode 4, when the Doctor is in the Whomobile, a dark cylindrical object passes in front of the camera in the foreground. It's not something of the Doctor's, as his hands are inside the vehicle.

Continuity: In episode 3, Sarah is hit on the head by debris knocked loose by the escaping dinosaur. It hits her on the back of her head or shoulders – but the later bruises and scratches are on her forehead.

Revealing: In episode four, when the Doctor is being herded through the complex, the walls wobble very badly whenever the metal shutters slam down.

Revealing: At the beginning of episode two, the soldiers firing at the dinosaur are aiming up and well to the left of the creature.

Revealing: In episode three, when the root attacks the Daleks in the mining area, the string holding the root up can be seen.

Revealing: During episode three, in the mining area, just before the city's root appears, the tracks on which the Daleks move can be seen.

Revealing: When the Doctor and Sarah arrives in episode one, they leave the doors of the TARDIS open and the empty inside of the TARDIS can be seen.

Plot hole: The temperature of the air being blown into the mines is controlled from the communications room when the Doctor needs to knock out the Ice Warriors. But conveniently, the ventilation system is controlled from the refinery when Eckersley needs to suffocate the miners.

Revealing: At the end of episode 2 / beginning of episode 3, the Doctor and Sarah are thrown into a pit. It is quite obvious that they hit a flexible mat when they land. it is gone when they stand up.

Continuity: In episode six, the Doctor is using the Aggedor statue to fight the Ice Warriors. The door the refinery was partially destroyed by the Ice Warriors earlier. But in every shot of Aggedor appearing or re-appearing, the door can be seen intact at the edge of the shot.

Continuity: In episode three, Eckersley turns on the security monitor. The very first image is of the entrance to the refinery, but it does not show the Doctor and Gebek trying to break in. Eckersley then flips through the images and finds one of the refinery *with* the Doctor and Gebek breaking in.