Tiredoldhack….. Using premium fares ex EURO is not only cheaper but also the fares have, in many cases, far greater flexibility than those purchased in the UK. As a result the issue of getting off in LHR and not using the last sector is actually quite easy to overcome. Simply change the travel date after the ticket is issued to a date in the future. It can even be linked to the next time you want to originate in AMS.
I have done this generally at the out station when coming home. Where the ticket offers such flexibility the only additional costs has been APD. However be careful of something called HIP (higher incremental point) which covers some fare types and can increase the fare to the LHR originating level. Most ticket desk staff will advise and there are some BA staff on this site who can provide the details.
Try flyertalk for details of this issue in the USA where some have been approached by AA in particular for taking advantage of cheap fares.
