Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,181
OP seems aware of the separate tickets issue and others have made good points about LHR logistics. I would add...
1. Surcharges are going to be quite high for Upper Class. ex-US is often higher than ex-UK as well. Any ex-GB leg is going to have high taxes as well. Adding in the additional cost of the flight to Europe is going to make this an expensive itinerary. Of course, if the OP's origin and destination don't have a direct, low surcharge option using an alternative mile programme, then this might not be entirely relevant.
2. If the OP is leaving from the west coast, then Upper Class is potentially worth it for a 10+ hour flight. From the east coast, the flight simply isn't long enough IMO.
3. It might be possible to book an economy or premium economy ticket with cash, including a European connection, and calling VS to upgrade the VS legs using miles.