(1) You can't turn them away anyway because they are travelling to the UK across the English channel.
(2) Some migrants could have been turned away before. The UK never imposed the toughest rules on immigration that were permissible under the EU. That's because Conservative politicians, on first name-terms with wealthy business owners, did not want to restrict immigration and upset business owners.
(3) Note that the UK has been moving towards a Danish model to impose tough immigration restrictions, and there is a massive outcry because apparently the Danish model is too punishing towards migrants and too strict... and yet, it seems to have completely flown over your head, and everyone else's heads, that Denmark is a country in the EU... ... ...