Hi,
Shipping methods apply to the whole order.
So if you want to be able to ship multiple products, you need to create more shipping methods with weight/volume restrictions for 2 products, for 3 products, etc.
I would recommend however a different approach, especially since it doesn't seem that you have a lot of products on sale:
Create two shipping methods, one for UK, one for the rest, and make sure that the "shipping price per product" option is turned on. Then, edit each product and under the "shipping prices" area, enter the shipping price for that product for your two shipping methods and that's it.