Found 24th May 2016
Did the Great Manchester Run at the weekend and got this promo code from the organisers. Scroll down to the bottom of the page and look for "Get Your Discount". May not work with some bookings, you'll have to try it and see, but 20% off their silly prices has got to be worth a shot. I booked returns to London from the North West and the 20% discount was applied both times.