Compound, transport to dock, await shipping, day or 2 on the boat, dock/customers clearance at UK, transport to dealer, dealer PDI. All that can easily take 6 weeks and 3 weeks at the very, very least I would think.
If you are distance buying you'll also find the dealers will do the 2 week cooling off period before they deliver the car. It seems a bit sneaky to me but I've always found that cars take at least 2 weeks after signing and returning the final paperwork. As I'm in no rush I plan on making that work for me this time. "Oh, I never received the paperwork".... "Did that not arrive, bugger! It must have got lost in the post, I'll send it again"