I've been getting into documentaries and it was said that the British had incredibly disciplined and elite soldiers, but also that they would often have terrible victories in terms of how many casualties (using losses in the title may have been confusing) there were against the rebels
Side question - were the scottish part of the GB army or just closely allied?
For your side question, the Scottish were part of the British army. At this point, England (which legally included Wales) and Scotland were all legally united into the Kingdom of Great Britain, due to the Act of Union 1707. However, King George III was also King of Ireland (which, while technically its own country with its own government, was essentially a protectorate of Britain), and Duke-Elector of Brunswick-Luneburg, aka Hanover (which, for historical and geographical reasons, had a much more seperate government than Ireland). Thus, as well as British soldiers, George was able to send German soldiers from his German possessions in Hanover. In practice though, most German soldiers were not actually from Hanover. About 9 out of 10 German troops were mercenaries from other German polities, like the famous Hessian mercenaries.