All the black teas in the UK are grown in places like Kenya or India. Some producers use different blends to give a different taste. Northerners and Irish tend to like a stronger slightly malty brew say by using more Assam style tea.
The type of water makes a difference to a tea. Some areas of the country I would not use tap water for tea making such as London, but some bottled Scottish water there. I find tea is better when I visit Teesside. I think there is less calcium in the water and less nitrates (common in agricultural areas). Fresh water is usually better as well so don't keep reheating the same water for tea. In Calcium reach areas clean the inside of the kettle as they scale up,