If you are planning on travelling to North-Eastern or Eastern Croatia, you will most likely find flying to the Hungarian airport of Balaton very suitable! Ryanair have flights from London Stanstead to this destination.

Travelling from Balaton Airport to Croatia
Upon landing at Balaton Airport, it is likely that you will catch a bus to the nearest train station of Balatonszentgyorgy, which is 12km away from the airport. From here, it is just a matter of catching a train to your chosen destination in Croatia - see the Die Bahn website for the best information about train timetables.

Useful Travel Links
Ryanair Flights from London Stanstead to Balaton
Balaton Airport Including information on getting to/from the airport
Die Bahn Train timetables for journeys from Hungary to Croatia
Hungarian Railways Also provides timetables for routes from Hungary to Croatia