Image link below:

The mixer taps on shower are having a delay (approx 20 seconds) when the
water is turned on then runs ok so suspect either the filters are
blocked or the cartridge is at fault. (already checked the shower
head/spray)
In any case I need to take the taps off to investigate.(Mira Coda shower)

Question: I need to undo the 2 nuts as indicated, can I just undo them
or do I need to support the tap assembly in some way to counter the
torque when spannering the nut?

If the filters are not blocked then what am I looking for with regard to
the cartridge (have only ever had old washer type taps before)

https://imgur.com/X58VnQb