England - What classifies as slander, libel. How could this be approached legally...

If someone had been court ordered to stay away from their own children (their ex partner has custody) due to various allegations of abuse from this person to the ex, and this person has now been elected as a town councillor. Would it be illegal or any sort of offence for me to write to the council addressing my concern at their ability conduct background checks (if it is something that is even checked).

Long story short this person should not be in a position of power at any level.

TIA