Strongbow, Magners, Bulmers, Blackthorn etc. are known as draught ciders. They aren't made with traditional cider varieties, so don't bother trying to source cider apples if this is what you're after. (Traditional English cider is called scrumpy, and you cannot find it in a Scottish pub. Believe me, I tried.). Draught ciders are typically 5% ABV and back-sweetened with apple juice or concentrate. If you do this, you will need to pasteurize your bottles. See here: http://www.homebrewtalk.com/f32/easy-stove-top-pasteurizing-pics-193295/
The only high alcohol cider you would find in Scotland is white cider, which is 7%+ ABV and generally made from less than 50% apple juice. It's mainly sold in grocery stores in 2 liter bottles, and plays the same role that malt liquor does in the US. You probably wouldn't find it in a pub, unless it was a real dive.