@Callum61 It is nothing to do with tax - It is your bank that will typically not allow short term renting without the right type of mortgage. Not sure what the 140 days is you refer to. I suggest you learn about Furnished Holiday Lets on gov.uk and see where you end up. Different rules apply for council tax/business rates.
It's very interesting to see STR policies in different countries. In the US, it's the STR policies in local municipalities, and the home owner insurance companies that provide the greatest barrier. There typically aren't any restrictions from mortgage providers if the property is the primary residence of the homeowner, but often there are some types of limitations stipulated if it's a secondary home.