I'm in the process of migrating fom BigCommerce, I can't believe how basic the shipping rules functions still are in Shopify. $15/month on an App to be able to control postcode based shipping rates... are you joking!! Fix this, go look at BC if you're unsure how!! and yes the UK is a nation of united Countries and Islands, all of which that need separate shipping rates/zones. I built my first Shopify Site, about 5 years ago, seems Shipping functionality hasn't progressed since then.. Wow!!