"And this was done to a part of Great Britain! The Act of Union made it such."

Ireland was never a part of Great Britain as such. It was part of the UK. The famine was pretty significant in part of Britain too though in the Scottish Highlands. The govt again reacted intiially far too slowly but this was down to their idealogy of laissez-faire (do nothing as the market will fix things)rather than wanting people to starve. When they were finally pushed into action they still baulked somewhat at giving things free preferring work schemes etc. Again their rigid ideology. Nothing more useless during a catastrophe than people in power who are convinced their way is correct despite all the evidence being to the contrary.

I read a lot of Scottish history volumes and the prevailing thought seems to be that the Highland famine didn't go into the apocalyptic scale of the Irish famine because despite it being during the Clearance phase the Highland landlords were still for the most part native and even if they were anglicised they still held some sense of responsibility towards their tenants. Likewise the Church of Scotland was the established native church. Organised charity often prevented it from being much worse than it could have been. On the other hand the ruling class in Ireland were the anglo-Irish rather than native and were more estranged plus of course the scale was simply more massive.

I think the Scottish famine of the 1690s (the ill years) which particularly hit the north-east Lowlands, was perhaps worse than the later potato blight in scotland. Some counties lost 30% of the population. People fled to the cities, fled overseas mostly to Ulster then perhaps across the ocean, or simply starved to death.