What usually takes the most time - causing it to take 3 hours+ to film a one hour show?
Probably the stop-start nature of the recording. The studio is deceptively small, and doesn't have that many cameras. So every time they move from one segment to another (eg, the power lap board, going to the news) there's a 10 - 15 minute break while they shift the crowd out the way, move all the cameras, check the lighting, and get the audience back into position.
This week they were showing the Peugeot Onyx which has reflective copper bodywork. It took ages to get the lighting just right to show it off properly. Even then Jeremy cocked it up, so they had to do the whole link again.
The news was about 20- 25 minutes long, the Lewis Hamilton interview even longer. Obviously, these will be edited down for broadcast.
Lewis Hamilton was 20 minutes late turning up as well. He got stuck in traffic apparently.