I think that UK weather requires the PPL to be somewhat pragmatic.
Much of the forecast information will give conditions which are 'conservative' - so frequently either the general situation will be better than forecast or specific aspects of it will be. I often note that the TAFs will oftne make a flight seem unlikely.
But - well there is always a but, now and then the shear variety of our climate will result in really much worst weather than forecast or localised conditions which really mean standing on the ground looking up is the only safe alternative. In about 300 hrs of proper cross country flying, I have made at least a dozen major diversions or U-turns and ended up on the ground omewhere I have no intention of being. I have also had probably a similar number of occasions where I have delayed leaving by at at least a day.
So as a 'dispatch rate' it starts to look like around 10% of my VFR cross country flights have had major alterations - but I do live in Scotland and by cross country I mean in excess of 2.5hrs..
But then even for 'local' flights I have had at least 5 major diversions in around 800 hrs - so approaching a 1% rate when you can simply look out of the window (mainly haar and localised rain / hale / snow).