No, you're OK, your dimmers are two way switches, so no problem.
will get back to you!
wrong - I jumped the gun!
I've just realised the crabtree switch is an intermediate switch, so you presumably have yet another light switch on that circuit (Ie 3 light switches for that light altogether)
The easiest way of dimming that circuit would be to put a dimmer on one of the other (hopefully 2-way) switches controlling that lamp.
You can get a dimmer switch size module which is an intermediate switch, but is not a dimmer. It would have these 4 connections, and its button looks like the others, but it is just operates as a push switch. Then the dimmer you have taken out, fit in one of the other light switch positions, if that is practicable for you.
This appears to be your old switch (slightly newer version):
View attachment 106037
And could be replaced with:
This is illustrative of the 'dummy dimmer' intermediate switch needed to replace the old crabtree switch. The wires would transfer to the same positions on the new module:
Intermediate Push-On/Off Switch Module (Dummy Dimmer) 6ACan be used to replace dimmer modules in existing faceplates or in the Matrix dimmer grid system
www.electrical4less.co.uk