The existence of Bigfoot (Sasquatch) in North America remains definitively unproven to this day. There is plentiful circumstantial evidence, some more compelling than others, however definitive proof remains elusive. This is problematic for a number of reasons. One could make a good argument why proof has yet to be found in North America (USA and Canada) based on shear size, however the situation in the United Kingdom is different.
There is a rule of thumb for the long term success of a species and its the 50/500 rule. I say rule of thumb, it does have a basis in science but these things are not exact and vary between species. So the 50/500 rule proposes that in order for a species to avoid inbreeding there needs to be at least 50 adults. Otherwise the effects of inbreeding will likely cause damaging mutations in the short/medium term. That is the 50. In order to avoid damaging mutations due to genetic drift a species needs 500 adults, that is the 500. There we can assume that for a species to be successful in the long term then it definitely needs 50 adults but really more like 500.
That is not really that many. There could be ~500 Sasquatch running around North America without people running into them all the time. Or at least not running into them to the extent where their existence becomes obvious. It is still perhaps perplexing that even with the number of people looking for Sasquatch no one has definitive proof. Especially as one would assume that they are in roughly the same areas. The North American case is however not was we are interested in today.
Why Not in the UK?
The United Kingdom is a difference matter. Here the population density of people is so high that is pretty much inconceivable that we would not have come across a breading population of Sasquatch by now. Their presence would have come to our attention. It is not just them themselves, they will have a footprint beyond simply that of the soles of their feet. There would be evidence of them feeding, sleeping, and moving around etc. Added to this that there are no large areas of isolated woodland in the UK that are not being frequently visited by people. The likelihood of an as yet undetected population being somewhere is sadly very small indeed.
Let us suppose that there have been sightings, which although I feel is unlikely, lets assume it for now. These must be sightings of isolated individuals that could theoretically be the remainder of a once larger population. This might explain the history of sightings in the UK, and also the odd contemporary sighting. People are seeing remnants of a almost extinct population.
What About Scotland?
In the UK Scotland, particularly the areas around the Cairngorms and the West Highlands, are perhaps the only exception. Even these areas do not seem very likely, but they might offer a last refuse to Sasquatch. These areas are much more isolated, and less people frequent them, and when they do they are in lower numbers. They are not empty however, so it would have to be a small population, and I still feel that it would have been discovered by now. One would expect that enough interest from sightings would eventually lead their discovery. These areas are also not vast areas of woodland, they, like the rest of the UK have been extensively deforested.
So the balance of probabilities is against Sasquatch in the UK. Evidence would have been found by now if they were there. If they are here in very low numbers then they are likely going extinct due to population and habitat fragmentation.