Extract of the terms of use:
The voucher can be redeemed between 01/02/2011 and 28/02/2011.
Travel must be between 01/02/2011 and 30/06/2011.
Vouchers are only valid for itineraries where all flights are operated by Lufthansa, Lufthansa Italia and Lufthansa Regional Partner (incl. Lufthansa City Line and Eurowings).
The voucher is only valid for flights departing in United Kingdom


https://promotion.lufthansa.com/ihg-2010/