I was on the P&R going into Cambridge whilst 4 months pregnant and on crutches. I was offered a seat (more for the crutches), but the driver pulled away before I could sit down. When I had words with him, he said he is not required to wait until people are seated.
I told him that I had fallen over and lost the baby, I would have sued him.
At 6 mths pg I was on the bus at Gatwick, and noone offered me a seat, even when I had asked! DH and 10YO DS had to stand one each side and hold me up and make sure I didn't fall over when it cornered (mad driver as well).
One point about pushchairs though. I have lupus, and am registered disabled (blue badge and all), so on the rare occaisions that I P&R into Cambridge on my own, my joint problems mean it is impossible to fold the pushchair and hold onto baby at the same time (I even have trouble doing so when I dont have the baby).
Parking in the centre is £4 an hour, with no concession (except for the first hour - can YOU shop in less than hour once you have parked? - and to get the concession you have to hold up queue of cars leaving to show your badge)
Just a thought!