It discusses York (Regional Municipality) v Winlow, 2009 ONCA 643.
The case is interesting because it deals with the fairly common scenario where police detect a motorist speeding but book them for a lower speed than they were allegedly travelling at.
In Victoria, the power to amend a summary charge is found in Magistrates’ Court Act 1989 s 50 and Criminal Procedure Act 2009 s 8. Those provisions say nothing about increasing the speed alleged (or increasing any other detrimental allegation contained in a charge. But nor is it open slather: amendment applications are typically permitted only when they do not cause unfairness to the accused, or amount to alleging an entirely new offence outside of the statutory limitation period.
The Court of Appeal approved the practice in Ontario of ‘amending-up‘ a charge if the motorist contested the ticket, holding it was appropriate for the prosecution to allege the detected speed rather than the speed the driver was booked for.
The Ontario Court of Appeal considered ticket-undercharging a form of plea-bargaining.
 I do not consider it inappropriate when a police officer uses discretion to charge a driver with speeding at a rate less than the actual rate over the speed limit. In a sense it is a form of plea bargaining. Normally, the prosecutor engages in plea bargaining with the defence. If a police officer charged a person with speeding 30 km per hour over the speed limit, and the prosecutor said that the charge would be reduced by 15 km if the person pleaded guilty, no one could seriously object. Plea bargaining by the prosecution and the defence is as essential to the effective working of the provincial regulatory system as it is to the effective working of the criminal justice system.
 In this case, the police officer, not the prosecutor, initiated the plea bargaining. Many offending drivers no doubt welcome receiving this “break” from the officer, without having to go to court to obtain it. Systemically, many cases can be disposed of without using valuable court time and resources. Indeed, I expect that the large number of speeding charges, the heavy volume of traffic cases before justices of the peace, and the desirability of finding an efficient way to deal with many of these cases has prompted the practice now before this court.
 However, when drivers, as is their right, decide not to plead guilty and pay the set fine, but to instead defend the charge at a trial, different considerations come into play. The prosecutor then has carriage of the charge against the defendant. The prosecutor’s carriage of the charge includes the discretion to manage the prosecution in accordance with the statute.
The Victorian Court of Appeal once frowned on plea or charge-bargaining (though the specific thing it was disapproving was discussion in chambers between advocates and a trial judge): R v Marshall  VR 725.
But since then the legislature, spurred on by the courts, has specifically enacted pre-hearing negotiation provisions, first in Magistrates’ Court Act 1989 Sch 2 Clause 3A, and now in Criminal Procedure Act 2009 s 55.
There might be scope then in Victoria for the Canadian practice of amending-up when speeding tickets are contested.
I wonder if the same argument might carry over to the case when the police see someone speeding and, say, not wearing a seatbelt, but only book the driver for the speeding offence. If they elect to challenge the ticket, can the police lay charges for all the alleged offences?