Thanks for the tips at parking at LTN Parkway, worked out great and went very smoothly, £12.40 for three days parking and £3.40 for the bus to the terminal.
Beats the £30+ Airparks and the other providers wanted for a weekend away.
My concern was that the car park would be pay and display and had to by a new ticket for every 24 hour period, but this was not the case and you just pay on departure.