I renewed my train season ticket yesterday and got over £300 off. No special discount, just 50 or so penalty vouchers for running late or the last year for both me and April.
They didn't make it easy either. In all it took around 30 mins. First I had to fill in my details on the back of each ticket. Then he scanned the barcode on each and wrote something on the back. Once that was done he then feed each into a machine that I'm not even sure what it did.
Still had to pay £3,500 though. Not really worth it.