tallboy, welcome to FT and the QF Forum.

We don't know the date you want to fly, but in June BA bas flights LHR-ATH for as low as 46 GBP each way. But note that the cheapest fares are for a horror 1:15am arrival.

You could ask about using IB via BCN or MAD as an option. BA and IB are the only two OneWorld airlines flying into ATH.

Some flavours of the Eurail passes include ferry connections between ATH and various ports in Italy and possibly other countries, so that may be an option if you are also looking to use trains to commute around Europe.