East Midlands are offering £10 off travel on any of their train journies via this link.
They travel from Luton Airport to London St Pancras, so are a great option for getting to central London quickly from Luton (which is not in London, despite what their marketing team would have you believe).
The relevant terms and conditions are as follows:
You must book by May 31st
You cannot use it for First or Standard Class Anytime tickets or London Day Out tickets
The voucher CAN be mixed with Railcard bookings
A return from St Pancras to Luton Airport costs £23.50, so this voucher brings that down to £13.50 (a 43% saving).
To save the maximum amount, you should book the return trip as two single journeys. Standard single price is £13.50 each (or £9.40 off peak, although I had technical problems on the test booking of a £9.40 train: possibly because it is less than £10), so these would become £3.50 each, meaning you pay no more than £7 return (you will of course need to get the voucher twice, by providing two separate email addresses).
I appreciate that flying to Luton from Malta means you’re flying Ryanair. As such, I feel duty bound to point you to this excellent Ryanair Survival Guide (it’s a couple of years old so some of the pricing is a little out of date: the other thing I have to add to it is booking seats on a Ryanair flights is, in my view, one of the best €10 you will ever spend).
(With thanks to Raffles at the Headforpoints blog for spotting this one)