If you are flying from Chicago to Franfurt via London via Heathrow Airport your travel agent will advise you of the minimum 'transfer time' required at Heathrow. Virgin operate out of Terminal 3 at Heathrow whilst Lufthansa operate out of Terminal 2. You do not have to clear customs at Heathrow, if you have 'checked in' at Chicago for Frankfurt and your baggage tags are for Frankfurt. Upon arrival at Heathrow Terminal 3, you follow the 'transfer' signs to the 'transit lounge'. In the transit lounge there are various airline desks. Go to the Virgin desk and get instructions from them (they will also be able to help if there is a delay on your Virgin flight or the Lufthansa flight). A safe minimum transfer time is 2 hours (it can be less-but better safe than sorry!). As Heathrow is in a state of 'flux', especially with the Terminal 5 opening at end of March, a lot of airlines are moving terminals after then-hence my suggestion of going to the Virgin transfer desk first. The other alternative is to take the transfer bus from Terminal 3 to Terminal 2 and go to the Lufthansa desk!! I hope you understand this??