Also the metars are specific to within 8km of the reporting aerodrome, so what weather do you take into account to apply the rule? A forecast which may not be accurate, a metar for the nearest airfield or your own estimation considering you may not be a qualified met observer or forecaster?
How about the weather that you observe by looking out of the aircraft windows and seeing whether you can see the ground or not. You don't have to be a qualified observer or forecaster to be able to make that decision.
Rocket science it aint - it's up to the individual concerned to make the decision as to whether he can or cannot comply with the privileges of his/her licence based on the conditions at the time - and if he can't then he has to do something about it to change that to compliance.
Maybe that's the problem with questions like this. People start trying to find loopholes in the way the rules are written in the ANO, rather than interpreting them in the spirit in which they were written. Let's face it - you'll only get hung if it goes pear shaped, but the best way to stop it going that way is to fly defensively, constantly evaluating your decisions against the conditions around you. I'm all for making a plan and sticking to it - but you should always have options and escape routes too. Arguing about whether 1/8 cloud holes is or isn't compliant is not, in my mind, a safe escape route.
An example. Saturday I got airborne, was in cloud at 600'. I was on top at 1200'. As far as I could see a completely unbroken layer - until I looked straight down, where there were small holes. Now, by some reasoning it could be argued that I was compliant. I on the other hand would say I wasn't because I don't fly looking straight down all the time (at 160 Kts that would be pretty dumb
) and on looking ahead and around the ground was not
continuously visible. It would not have been legal or sensible for a UK PPL with no extra ratings. He may have been VFR on top, but there comes the question of getting back down again - and you can't stay VFR if descending through cloud which has more than half cover as you're going to fly through some in the descent sooner or later.