I love travelling in Europe and have visited many times, however this itinerary would be too ambitious for me. There is so much time spent travelling that I would feel like I am missing out (and I don’t think one night in Spain is enough).
I would either spend more time in each location OR change the cruise (if refundable) to a med cruise return from Southampton (great one at the end of June) OR skip London or Paris for next time.
If you are definitely set on this itinerary, I prefer Eurostar to flying from Heathrow/Gatwick.