Depart Kefalonia 1215 this Sunday
Arrive Gatwick 1335.
�207 per person.
That appears to be the final charter flight of the season with Monarch:
http://flights.monarch.co.uk/
Or:
Tomorrow, 1445 ex Kefalonia, arrives Luton 1620, �66.71
Thursday, 1240 ex Kefalonia, arrives Manchester 1430, �61.71
Thursday, 1600 ex Kefalonia, arrives Gatwick 1730, �71.71
4 Sept (Th), 1240 ex Kefalonia, arrives Manchester 1430, �116.71
Those look like the final flights of the season with ThomsonFly:
http://www.thomsonfly.com/en/index.html
Those appear to be the last direct flights available in 2008. That's based upon searching all of the relevant airlines listed here:
http://en.wikipedia.org/wiki/Kefalonia_Island_ International_Airport
Your only alternative would appear to be to travel via Athens. Aegean are relatively expensive for flights in the near future. (e.g. �369 + taxes this Friday) but quite cheap later on. (e.g. �157 + taxes on Sunday, 28 September). Their flights typically have a 3� hour connecting time in Athens, before taking you on to Stansted.
http://www.aegeanair.com/
Olympic are also quite expensive for 'short notice' flights but they're offering �165 for Kefalonia-Athens-Manchester later on. (I tried a random date in October).
Chris