Booking both legs together
Arranging the return pickup at the same time as the outbound journey means one less thing to think about while you are away, and some operators offer a modest discount for booking a return rather than two single trips. Confirm the pickup point at the airport, since this can differ from where you were dropped off, and double check the arrangement closer to your return date if your flight time changes.
Book with a local operator
Browse airport transfer firms in Milton Keynes and ask about return bookings when you arrange your outbound transfer.