Having found a poster at the station saying the stop had moved to the main road, I went there and just missed a rail replacement bus departing at 15:26. I assume this was the 15:40 I was aiming for, as I waited for over half an hour (no bus arrived), before my mum drove me to Whittlesford Parkway, where I got the bus at 16:15 to Audley End, arriving at my final destination 43 minutes late. I don't believe this qualifies for delay repay (either because the journey involved a rail replacement bus, or else because I went to Whittlesford Parkway by car), but could someone confirm this please?
EDIT: I was travelling on a split ticket (origin station - Whittlesford Parkway return, and Whittlesford Parkway to Shelford return - so effectively the return portion of the second ticket was not used)