I would advise anyone with doubts about their own ability to not fly. That's the simple scenario.
However, there is the argument that when you've had your training (and not many people get a lot of change out of £10k by the time they've got a PPL and a few hours), you ought to use it. If you don't use it, you will eventually become more and more nervous and will stop flying. This is probably a large part of the reason why some 90%-95% of PPLs never make it to their first license renewal.
It is difficult to argue this line though in the face of the safety argument. It's a bit like debating speed limits. The higher they are, the more deaths there will be, and human life is priceless, so logically the speed limit should be zero. QED. Or perhaps 5mph, to be really generous. The aviation equivalent is flying only in perfect sunshine in a 500nm radius, and I've already said above what that leads to.
The big problem for a PPL in the UK is that if one takes every TAF literally, one would not fly for perhaps 3 months in each year. There isn't a lot that can be done about that, because unless one can fly on instruments, one's options are very limited. If I was a PPL only I would not fly anytime the TAF for the relevant areas has a cloudbase below the MSA... I do believe that PPL students are short-changed in not being told this sort of thing at the outset although commercially I can understand it.
But the converse applies: if the forecast cloudbase is OK, the METARs are fine, etc, and the plane has the range to make a decent weather diversion (say 2hrs reserve), then one should just get on with it. Bring an extra pilot along by all means - always a good idea for someone new.
But as I keep saying, of all the reasonably reachable things, nothing will do as much for one's ability to fly on a given day as an IMC Rating (with currency, and access to a decent plane).