It also states on the BA website - I assume on the same page - that Speedlink has been incorporated into National Express. Obviously this removes the pricing issue (and is a sly way of hiking prices by £3)

As BigLar stated, he got a discount last September, but a bit of looking suggests the 'merger' took place on October 1st and there have been changes to the pricing structure - including staff discounts - as a result of this.

I have a discount code for 10% off National Express - SWISSTEN - not sure if it still works, but might be worth a go.

And to reiterate the earlier point, I would ensure you spend as long at LGW as possible - the airport, unlike LHR - is open for flights 24hrs. If you arrive at LHR at 3am, you may well find yourselves locked out of the buildings...