Official Kosher sandwich guide at London airports
...for those of us who do not have reliable access to BA First Class lounges.
The list is straight from 2010 edition of KLBD kosher food guide. Needless to say availability/variety may not be guaranteed.
Heathrow T1: AMT Coffee landside (DD's), Caffe Nero airside (Adafina)
Heathrow T3: AMT Coffee and Bite Cafe, both landside/arrivals (DD's)
Heathrow T4: Caffe Nero landside (Adafina), AMT Coffee landside (DD's)
Heathrow T5: Caffe Nero landside (Adafina)
Heathrow central bus station: Caffe Nero (Adafina)
Luton: Food Village landside (DD's), The Real Food Company airside (DD's)