Any filtering system will be imperfect because (among other reasons) anyone in the world can use a web address ending in .co.uk (as many Chinese vendors do), whereas some UK businesses may choose to host their websites overseas.
However, you can refine Google search results by clicking on 'Search tools', then on 'Any country', followed by 'Pages from the UK'.
google the search item ie Crosswords -when the results come up directly above the first result you will see a horizontal menu -one of them is 'search tools' click it and it gives you the choice to filter the results to any country you wish -click UK and only UK results should come up. it will stay on 'UK only@ until you change it back.