Can I visit Scotland with a UK visa?
Yes, of course you can since Scotland is part of the UK. The only part of the islands that you probably can't visit with it is Eire - the southern half of Ireland, which is totally independent. I'm not sure about this but I believe you could also visit the Isle of Man despite its having its own parliament and laws independent of the UK.
Yes you can. Scotland for the time being is part of the United Kingdom. Thats not to say that the circumstance may change in a couple of years.
If Scotland becomes independent then a separate visa will be required but please dont be downhearted I am sure that an outward looking Scotland will welcome you. I can not speak for England.
Yes. Scotland is part of UK. UK means England, Wales, Scotland and Northern Ireland