I booked one of those cheepie tickets over internet to SFO from LCY (LCY-AMS-DTW-SFO). I missed my LCY to AMS flight by 15 minutes. The ticketing agent at LCY called up KLMuk reservations at Norwich and I was rebooked on LGW to DTW later that afternoon with a later connectionto SFO. I was charged £50 rebooking fee.

Good Luck.