Megamiles,

I'm sure you can find a great deal as HEL-LON-HEL is only about 80GBP, so why not in reverse? Besides, HEL is just 50 miles away from TLL and a lovely 4 hour ferry or 1,5 hour catamaran ride is only another 5GBP an upwards. Also, you don't need to go back via Estonia as return flight from Australia goes via London. Just throw away the LGW-TLL coupon or use it at a later date.