He confirmed that the script from the first Hobbit film, which will be directed by Guillermo del Toro, has been completed and turned over to the studio.
"The Hobbit will be two movies and we've written the first script and delivered it to the studio who seem to be happy with it," the New Zealander told reporters.
"We're now halfway through the second script and Philippa, Fran, Guillermo and myself are doing the scripts and having great fun."
He continued: "It was an interesting experience because eight or nine years have passed since we wrote the Lord of the Rings screenplays and I was worried it'd be weird or hard or uncomfortable to go back there, but as soon as we started writing the scripts it was fun, actually, and easy."
Jackson also said he had been scouting for locations in New Zealand immediately before travelling to London.
He stressed that there would be continuity between his films and Del Toro's, despite the latter being better known for macabre material like Pan's Labyrinth.
"We're writing the screenplays with him, so in terms of the script, there is continuity," he said.
"We're writing Ian McKellen's dialogue just the same as we did in Lord Of The Rings. But Guillermo, being the director, will obviously take the script and interpret that and shoot his film. So that'll be interesting to see.
Jackson confirmed that the Hobbit films will not be released in 3D. "Guillermo wants to shoot in 35mm, old-fashioned film, which suits me, because he wants to keep it in the same space as the original trilogy."
For the latest update on The Adventures of Tintin: Secret of the Unicorn, Jackson confirmed that the Steven Spielberg film is in the can, but will take two years for the computer animation to be completed.
The The Lord of the Rings director said "Tintin is great. It's made. The movie is cut together and now [we] are turning it into a fully-rendered film".
"So the movie, to some degree, exists in a very rough state."