Like I wrote before, I have a Samsung Full HD TV which is also a smart TV which allows me to watch catch up TV from the terrestial channels without needing a set top box but obviously it needs a broadband connection. It also allows me to watch things like my Youtube channel on my TV too.

If 4K does improve the TV picture without programmes/films being filmed in 4k then maybe people should look at 4k, but going by the limited 4K pictures I have seen so far, its not worth it unless the sky box providing the pictures is not Sky HD.

Putting aside the differences in quality of various sets, it is simply impossible for a 4K tv to improve an HD picture. The tv is receiving a 1080 HD picture and cannot increase the amount of detail you will see. Arguably it could be worse than an HD set because it is having to scale everything up to fit the screen.
To see 4K properly you need Sky Q (very little content available yet) or 4K blu-ray for example. Even then to get the full benefit you need to sit much closer to the set.
A high quality HD set would be my preference if I was buying now, but they seem to be harder and harder to find because manufacturers are too busy plugging the latest gimmick.
I'm not sure if 4K broadcasts will ever become widely available, and I'm certain most people won't notice the difference anyway, so I'm sitting this out until things become clearer.

Even some 4k UHD blu-rays are upscaled from HD so you're not guaranteed a "real" 4k source from that.
The main difference between HD and UHD will probably be the wider colour gamut - and high dynamic range which together bring a noticeably better picture than just more pixels.
However, the standards for that are too new so it's probably best to wait a year or two for it all to settle down. By then, though, the manufacturers will be on to the next gimmick...sorry, improvement.