From
https://www.tt2.co.uk/help/prosecutions-code/Alternative to prosecution
We may offer you a warning (on condition of payment of the unpaid toll notice charges) as an alternative to prosecution.
If a warning is offered, this will be confirmed in writing and the person can avoid prosecution by complying with one of the following conditions:
a) Pay the unpaid toll charges in full, OR
a) Set up a payment scheme and pay agreed minimum amounts within the time periods specified.
If a warning is offered and the conditions are not met then we will continue with our investigation, which could lead to you being prosecuted.
I'm pretty sure that if I started writing to people demanding money in exchange for not prosecuting them, I could end up in a spot of bother? Can a prosecutor, absent statutory authority, accept a cash payment in exchange for not bringing proceedings?
I suspect the difference is that the toll charges have a statutory basis (I assume) and it’s not just a bribe not to prosecute.