This depends where you are in the world and where you are applying to.
If you're applying to a course in Scotland the 4-year degree takes students in from school usually without a Foundation. Check the entrance requirements. You might feel that you still want to do a foundation course so that you know which subject you'd like to apply to however if you have the grades at A level or Advanced Higher you'll be qualified without a Foundation Course.
If you're applying to coures elsewhere in the UK, you will usually need to do an art foundation level course first. Some courses don't ask for one but my opinion would be that the ones worth applying to do ask for a Foundation Course.
Even if you are in Scotland, you might be best to apply for an art foundation course as well to cover all bases – just in case you don’t get into a degree programme as it is very competitive.