Goofs

When, towards the end, the characters are running up the staircase inside the tower it is obviously daylight outside. In addition there are candles in some windows yet from the outside the are no lights.

The arrangement of the windows seen on the inside of the tower as they run up the stairs doesn't match what you see of the tower from the outside.

New Zealand doesn't have submarines.

Coming from night in Cumbria's winter, they should emerge into daylight in New Zealand's summer, yet not only use it might but by their breath you can see it's winter in NZ.

(at around 51 mins), during the pouring of the spike in the foundry, Griffin breaks the "fourth wall" by briefly looking up at the camera and then quickly away again.

Griffin emerges from the tunnel with his face illuminated from above; the others then appear to be lit by sunshine in the tunnel but then they all emerge into the pitch blackness of grassland (although it is cross-lit briefly).

Unsurprisingly, the area around Ruapehu, with its three volcanoes, looks very little like Cumbria which doesn't have volcanoes or the vast open plains of the Central Plateau.