Excuse this small rant from one of the far corners of the Kingdom, but I hope you find it informative
I’ve noticed of late there has been a more common use of the postage costs for parts and the like stating “UK Mainland”. Can I point out the the good old GPO still uses the Universal rate for the whole of the UK. Now if you prefer to go Courier they do charge extra for Highlands & Islands, but in my experience Royal Mail/Parcelforce offer as good as service to the outer fringes.

