I picked up from Brent Cross last Wednesday. They've only been doing collections for two weeks so it's a new process for them.
Here's what happened to us.
We arrived about 20 minutes late (due to a delayed train), but found the showroom on the ground floor without issue. Introduced ourselves to the sales advisor who told us that since we were late, they'd given our car away.
Sales guy headed out the back to find the delivery guy, who appeared a couple of minutes later, then he walked us throught the shopping center to the lifts, and took us to Red car park, level 4. The car park was empty other than a couple of demo vehicles, and three model 3's waiting for collection. The guy showed us around the car - confirmed that the charging cables were in the boot, then we got in the car, and he spent about 40 minutes going through the details - telling us about all of the settings. Once we were happy, he had me sign on his iPhone, then left us to it. We told him we were going to get something to eat before we left, and he said that if we though of any questions while we were eating, to go back down to the showroom and ask for him.
Overall, a really good experience - not at all rushed, no videos.
Hope that helps,