South Shields is not taxable as world income by the Poland tax office
There is no world income only single agreement country with country. There are some countries which don't have such agreement with Poand or less favorable and then Pole has to pay tax if he lived there.
The difference in the tax-free allowance between the two countries must make many Polish people gasp in disbelief when they arrive
that what you say is how countries treat less fortunate - lower earning population. So many Poles while moving to UK and taking lower payed jobs are gaining double: 1st because they move to higher wages country and 2nd because they benifit tax exempt for poorer people. If somewhone is earning well, then more important than tax free amount is total taxation (as bigger chunk of their salary is not tax free anyway).
Poland does however have one big plus as far as tax is concerned: liability for tax generally (there are a few exceptions that affect almost nobody) kicks in at 183 days per year rather than the UK's 90.
Are you saying that if British spends 90 days in UK and the rest in Poland then he has to Pay tax both in UK and Poland?
Also how do they count the 183 days? Because different countries have tax year in different months. (not from January 1st to December 31).