Lets get this right. You have an RCB which is the "main" incoming switch
for your consumer unit and an MCB for the ring circuit.

Correct

That on occasions either the MCB or the RCD will trip if you turn on a
workstation.

Correct

First of all when you say "turn on" a work station, is power already going
to the PS and you're hitting the (soft) start button, or are you turning on
the switch on the PS itself? Secondly does the MCB trip with just one or 2
workstations connected? Are all the workstations the same?

I have a number of workstations, any of them has been known to trip
either breaker - they are less prone to trip if they are turned on via
the wall socket and then via the soft start.

All have 350 - 450W internal PSUs.