I do not think that you have thought this through. Of course, the resources issue is crucial. The problem would not be that Europeans would have to queue longer. It would be that the airport would be unable to operate safely due to excessive crowds. You would have to either redesign the airport and substantially increase the number of borderforce staff (assuming that you can find that staff, which is very far from a given) or reduce the number of people allowed to board UK-bound flights (in other words, reduce the number of flights). It would be a colossal example of inanely stupid policy of the cutting-your-nose-to-spite-your-face kind.