The only international flights at Fukishima Airport are from Seoul (Asiana Airlines/ All Nippon Airways) and Shanghai (China Eastern Airlines).
Domestic flights serve Fukishima from Sapporo (Hokkaido International Airlines / All Nippon Airways) and Osaka (All Nippon Airways / Ibex).
Since Asiana Airlines fly from Heathrow to Seoul, that might be your best route. (Korean Air also serve Seoul from Heathrow, with a service from Gatwick due to start on 27/03/12).
Confusingly, Sendai Airport is actually slightly closer to Fukushima than Fukushima Airport is. Asiana Airlines also fly from Seoul to Sendai, so that's another possible route. Other international flights into Sendai are with Air China (Beijing, Dalian & Shanghai - all starting 25/03/12), Continental (Guam) and EVA Air (Taipei).
It might be easiest though to simply fly from the UK to Tokyo Narita Airport. From there you can take a domestic flight to Sendai (with All Nippon Airways but operated as either ANA Wings or Ibex) or the train to Fukushima (90 minutes).
Chris