I can't really comment on the forecasting accuracy of the Royal Met Office, as I don't work in the UK. I stumble every now and then over one of their TAFs, when briefing pilots for flights to the UK and my experience so far has been, that UK TAFs are decent enough and often lean a bit towards the pessimistic side - just like ours.
With regard to the mentioned TAF - when I saw it, I at first thought it was a fake, because I can't seem to remember a TAF with so many overlapping TEMPO groups. However, I had a closer look and thought it looked like a situation with low stratus and warm advection aloft.
As I'm writing I still have some UK surface observations and some vertical soundings from the 30th available on my workstation. To me it looks like a vast part of England and the better parts of Wales and Scotland (except of some regions on the leeward/western side of some prominent hillridges) were covered with low stratus. In the Newcastle area it reached up to 5000 ft msl at noon, with other layers higher above. Indeed a southeasterly current e.g. at 5000 ft msl brought warmer air to the UK.
This weather pattern often is associated with drizzle falling out of the low stratus - with rapidly changing intensity and equally rapid changes in visibility and cloud base.
So I can understand, what was the motivation behind this TAF. A pity I don't know for which airport it was made. My guess would be Aberdeen, but I will probably err on this. Else I could have told you, what really happened in that period.
The highly complex computer models, that try to anticipate the state of the atmosphere ahead in time are fairly good in predicting the shifting and change of large weather structures, but at least the ones that are available to me do a poor or at best mediocre job in understanding, what will go on in the boundary layer of the atmosphere, say below 5000 ft above ground. Especially with regard to haze, mist, fog, low stratus and drizzle or snow grains.
So sometimes a forecaster can only recognize the potential for hazardous conditions, such as heavy drizzle with poor visibility, but he hasn't got a reliable guidance as to when this phenomenon may occur precisely. As others have already said, local experience may be of help, though.
Anyway, I don't agree with you, that this TAF is useless.
APRIANAs interpretation is spot on in my opinion. The MOST PROBABLE weather condition is expected to be 6 km visibility and 900 ft ceiling at this location.
So with the first group that states the basic weather conditions you already have a good idea that crosscountry flying VFR in a fixed wing plane may be problematic in this area. Especially in somehow hilly terrain. The various TEMPO groups offer quite a range for deterioration, so such a flight maybe outright dangerous as visibility and ceiling may drop even below the legal limits.
An IFR pilot however, who wants to operate into this field and has a limit of say 800 m and 200 ft ceiling can expect a pretty low chance, that conditions will be below his limit and also good chances, that conditions will be significantly better than that.
Somebody, who is desperate to practice some VFR patterns at the field may deduct from this TAF some chance to be able to do so, but as it is just PROB30 that cloud base will be better than 1000 ft agl chances are, that he or she will waste a lot of time, while waiting for sufficient conditions.
I think an individual weather briefing taylored to your special demands could in this situation shed more light on expected conditions for your flight, than this TAF can. In Germany, we still offer such briefings, mainly via telephone. The feedback from pilots so far has been encouraging.
One final note with regard to computers - 12 years ago work as a MET officer - at least here - was still exclusively a paper and pencil job. I just want to talk for myself, but since the advent of modern computer workstations I have been able to visualize weather data and which enabled me to absorb a vastly higher amount of weather related information in a very short time. This has improved my understanding of weather patterns enormously. I daresay, this has also considerably improved the quality of my forecasts and briefings in the past 8 years. More than can be accounted to the improvements in resident numerical modelling, to choose my words very carefully.
I hear the same from other colleagues, that I regard as competent.
I'd be also highly interested in feedback to the original question from pilots and meteorologists alike.