Richard Hammond set off the metal detector at the airport because of pins in his knee from injuries sustained in the Rimac Concept One crash in season 2.
Richard Attwood has driven in Formula 1 and Formula 2, as well as in endurance racing. During the height of his F2 success he was beaten only by Jim Clark.
Stansted Airport does indeed have a very long walk to the gates. The walk from check in to the closest gate is a quarter of a mile.
Permission to ride a motorized suitcase through Stansted Airport was needed from both the airport management and the Department for Transport, which is responsible for the security of UK airports.
The Porsche 917 variant driven by James May and Richard Attwood was the 917K. The K stands for "kurzheck", German for "short tail".