I would like to book AY - but this trip is turning to be a pain to organise. We will fly one way with ryanair and take rental car and spend week in UK, then go to heathrow and pick up in-laws >drive to london> drop car off.
Long and the short of it is that if we want to fly one way LHR>HEL - AY is 5x the price of BA, so BA it is.