T's 1,2&3 Heathrow (Death-row) is filthy, squalid & more like pre-modernised Mumbai with every visit, or a supersized Ahmedabad.
Manchester is just... crap. Poorly laid out, poorly signed & shambolic.
ANY UK 'International' airport is straight out of The Third World.
Sorry if it hurts or offends anybody but it's the views & opinion of 20 year veteran.