Sir David Attenborough has described the painstaking efforts of excavating the skull of a sea monster found on the Dorset coast as part of a new documentary.

Attenborough and the Giant Sea Monster follows the process of removing the huge skull of a pliosaur, one of the biggest carnivorous creatures the world has ever seen, from the Jurassic Coast.

The 150-million-year-old skull of the pliosaur was found on a beach near Kimmeridge Bay.

The documentary also uses CGI to show what the giant predator, which was the size of a London bus, would have looked like when it terrorised the seas in the time of the dinosaurs.

Sir David said: "It (the skull) weighs over half a tonne. That's a pretty heavy thing to handle.

"Now, you have to get it out from half way up the face of a tall cliff which itself is crumbling away, and if you drop it and break it, it is a major catastrophe. I mean, you will have lost a lot of information.

"So the problem we see in the first part of the programme was about is how on earth do you go around getting this out?"

He added: "There is no question about that. (It's) one of the biggest skulls you've ever seen.

"I mean, it's huge and so, although I was aware of the tip that was first discovered, I hadn't fully appreciated how big the whole head would be - and it's enormous.

"So sheer scale was what first impressed me.

"The thing about the skull is that it's not only by far the most informative part of the body, it is by far the most delicate too. And it's the detail, and that is so rare to find it. And this is as near perfect as it can possibly get."

He continued: "It could obviously move at great speed and the teeth that were found in the tip of the skull have vertical ridges down them, which break the suction and allow it to withdraw the jaw from prey quickly - that's the sort of deduction that we're able to make and which we show in the programme."

The documentary reunites Sir David with his long time executive producer, Mike Gunton, with whom he has worked on the Planet Earth series, and Sir David said Gunton was his first call when he learned of the discovery of the skull.

Sir David said: "I've been passionate about collecting fossils since I was a kid and I've never given it up.

"In consequence, I know a number of the collectors and people who live on the Jurassic Coast.

"One of them, Chris Moore, is a long-time friend, and he got in touch with us and said there's going to be a remarkable discovery that this thing had been found.

"I immediately rang up Mike and said, 'We ought to be doing this'.

"Fortunately, the BBC was able to do so - when the BBC decides that it wants to act, it can act very swiftly and very effectively. And we had a crew down there before you knew where you were.

"It looked as though it was going to be one of the most complete skeletons ever found.

"The head was only part of it, and that was up in the cliffs. And the body itself, being about the size of a London bus, extends into the cliff.

"The decision had to be taken that we would go for the skull, because that is where all the information lies.

"The rest of it probably has to be there but it's 30, 40 feet long, so at the moment we are concentrating on the head, the skull, the most important part."

Attenborough and the Giant Sea Monster will air at 8pm on January 1 on BBC One and iPlayer.