Hmm, seems your main destinations are Paris and London. You can easily daytrip to Canterbury and Stonehenge from London.
Lourdes is the tough one for me,, it is not a daytrip from Paris, but you can likely find a tour that runs from Paris down and back.
You can fly into London, spend 5-7 days( this includes the daytrips from London to Stonehenge and Canterbury) then, take the Eurostar to Paris( nicer then flying , only 2.5 hours city center to city center) spend the rest of the time there with a 2 day side trip to Lourdes( this is a guess, I would google a few tour companies from Paris to see if they do trips to Lourdes) then fly out of Paris. You could of course do this in reverse( fly into Paris and fly out of London,, which may be better as arriving at the Paris airport( Charles De Gaulle) is generally considered much easier then leaving( in terms of lines and signage in terminal,, many prefer not to fly out of CDG)Arriving is very straighforward and easy though,, I get through that airport pretty easily.
I will google a bit and see what I can see for Lourdes.My basic feeling is do the daytrips with a tour, but do the actual stays on your own,, far more relaxing and not hard to do .
