If a UK citizen residing in the Czech Republic receives a driving ban for a minor offence (not displaying a front numberplate) and he holds a UK driving licence, do the Czech authorities have have the power to revoke the UK licence and enforce the ban?
First of all, not displaying the front numberplate is by no means a "minor offence". It renders all kinds of automated traffic enforcement devices (speed cameras, red light cameras at crossings, etc.) completely useless. You could thus be speeding at will and ignoring all red lights without any fines, unless the police managed to chase you down.
A driving ban ("zákaz řízení") effectively renders your driving license useless in Czechia. If you ever drive again in Czechia while under such a ban, you're commiting a crime ("maření výkonu úředního rozhodnutí) for which you can be imprisoned for up to two years (plus removed from the country and banned from re-entering).
Such a ban probably has no effect on your right to drive in the UK (there would have to be an international treaty specifying that), but IANAL.
Czechia has the power to ban you from driving in Czechia. But Czechia cannot revoke your foreign license.
In any case Czechia could choose to notify UK about that offense and so UK will eventually decide independently and eventually UK will revoke your license.
This depends if CZ want to do something, UK want to handle the thing, and how minor UK will consider the offense. Often only major offenses go to the final step, but this is very dependent on both countries, and how each countries consider problematic an offense.