What would be the quickest/easiest way to get from London to Normandy region of France?
Where in Normandy do you want to be? It is quite a large department.
Jeanne: Your PM told me you want to visit the DD Beaches. Take the Eurostar (train) from London to Paris' Gare du Nord then take a taxi to Gare St. Lazare. From Gare St. Lazare you can take a train to Bayeux in Normandy. There are DD Day Beach tours operated by Battlebus in Bayeux which many extol highly. We toured the beaches on our own in a rented car so I have no personal experience with Battlebus.
Or you could rent a car and drive from Paris.