Sorry, my mistake mentioning Douglas. Part of my brain forgot for a moment that the IOM isn't in the UK.
I suppose I made another mistake too. I should have written "If you can find a single reference anywhere other than in your own posts on this thread to 'the midlands' in reference to the central part of the UK, I'll eat my hat."
I know what you mean by the midlands for the UK. As you said, you helpfully posted a map. But this doesn't justify the statement that it writing midlands without an initial capital letter "should be enough to let people know" that it's a reference to the midlands of the UK.
The Oxford English Dictionary only has an entry for Midland, capitalised thus. Similarly, Collins English Dictionary only has the Midlands, capitalised, and defined as "the central counties of England". Even in American English, I can only see a capitalised entry in Webster's, with the definition "the central counties of England".
I really don't believe anyone except you has ever referred to the UK as having "midlands". And that's probably because everyone would assume they meant the Midlands!