I bought a 41999 today at the LEGO shop in Milton Keynes. I live in London and on Saturday I phoned around LEGO shops in and near London. They had some at the Milton Keynes shop, and reserved one for me to collect today.
When I phoned the London Westfield shop, the guy I spoke to said something about them getting some 41999s delivered on Tuesday the 13th (tomorrow) and to try phoning them at about 12 noon to reserve one. I opted for the Milton Keynes shop since they actually had them in stock when I phoned. Anyone in or near London who wants a 41999 could try phoning the London Westfield shop tomorrow. I don't know how reliable the info was that the guy at Westfield gave me, but it's worth a try phoning them.