I've a general rule with spots like that (it's about two miles from where I live, by the way). If I can't find out how to get a ticket, or can't get one, I fish, and explain it to the bailiff, in the unlikely event of one turning up.
The worse that can happen is that you get kicked off, but usually you can broker a deal with the bailiff if you've done your best to stick to the rules.
That bit of the Nene isn't bad for trotting, but there are better bits much further upstream. The Kettering DAA bit at Thorpe Waterville's really nice; the river splits into two, one a streamy, shallow gravelly bit, the other slower-flowing and much deeper. There's a nice weir pool at the head of this stretch.
The Castor backwater's nice trotting territory - just drive through the bvillage (from Peterborough direction) then as you reach the last few buildings, turn left down station road, park at the end, and the backwater's right in front of you.
Finally, Alwalton is another reasonable trotting bit. Drive into the village, park at the village hall on the right, and then walk down the hill to the river. There's a tiny lane opposte the car park, too, which gives you some nice parrot-cage swims; great for roach on the seed/maggot. Some chub.