Hi A Fellow Flying Welshman,
I started my IMC training when I had a around 120 hours total time in a Tomahawk that I had flown many times before, it was in fact the plane I did my first solo in.
Found that basic attitude work including unsual attitudes were fine but when it came to holding on NDBs I totally lost the plot for an hour or two (I only really got to grips with the holds especially the entry when I did my FAA IR, thanks Martha King!!!).
As others have said as long as you feel comfortable flying the plane, that means you can hold the plane straight and level *with* spare mental capacity to do the other airmanship tasks then by all means start your IMC rating course.
Starting an IMC Rating course should be more than possible for the average pilot straight after your PPL, just look to the other side of the pond where some new FAA PPL's go straight into their FAA IR training under part 141 which doesn't require any additional time. And the FAA IR is by no means easy... the IMC rating is no where near as difficult or stringent as the FAA IR.
Just ensure you have the 10 hours P1 since your PPL issue to have the IMC Rating added.
Best wishes,
Charlie Zulu.