London to Bayeux then Paris

You can take the Eurostar to Lille. From there I would rent a car to get around the small towns and beaches of Normandy. Return the car to Lille when you're done and there are lots of trains that will get you to Paris.

Hmm that looks like a farther drive than if we took the Eurostar to Paris.

You may know already there is no public airport around Normandy. So London to Paris to Bayeux or Caen is the way to go.
Here is one DDAY tour from Bayeux on Saturdays
http://www.bayeuxshuttle.com/

Given the amount of time to get to and from airports,along with the required two hours ahead time to be at the airport before the flight, the quickest method between London and Paris would be Eurostar to Paris, transfer to St Lazare, and then a 2 hour 10 minute or so train to Bayeux, which runs several times a day. As for Overlord on weekends, the website instructs to contact them for the specifics of their schedule, many of their tours do apparently run on weekends. Overlords' full day tour was fantastic, by the way.

I can fly from London to Caen

That's new to me. Is there an airline on that route now? Which London airport?

I wound up using the Eurostar and train to Bayeux method described above. My other thought was the ferry from Portsmouth to Cherbourg but it seemed longer and more weather-dependent.

An even better option than my original idea would be to drive from Lille to Normandy and then drop the car off in Caen or Rouen or wherever is close in Normandy, and then take the train back to Paris (recommend Europcar). True its a longer drive from Lille to Normandy than from Paris to Normandy, but (a) the Eurostar gets to Lille an hour before Paris, so you could start an hour earlier; and (b) I would never drive in Paris, so starting from Lille saves that.

Nigel: Skyscanner.com tells me there is one non-stop flight in the middle of the day to the Caen airport from London. That depends on considering the Southend airport as London. Cheap, though, on flybe. . https://www.flybe.com/flights-from/london-southend/

Another option is to get a non-stop flight from London Southend to Caen on Flybe. It doesn't fly every day, but it is the cheapest and quickest way to get directly to Normandy. There are buses between the Caen airport and the city center, but I think the best connection to the train station is to take a cab.

cool.... Southend isn't a large (or even a medium) sized airport with a half dozen or so flights a day, mostly Easyjet - or at least when I tried it for my one and only time - and not especially well connected to London with the all-stops commuter trains going from Liverpool Street, but it counts as a London airport - just.

Nothing wrong with Flybe. Narrow body prop planes.

I've just had a look. The flights start approximately April First.

One flight a day only on Tuesday, Thursday, Saturday and Sunday. 11:35 Tuesdays and Thursdays, noon on Saturdays, and 10:05 on Sundays, only until the end of October.

The return flights are the same days, 25 minutes after arrival in France.

Thanks for the information! I think the flight to Caen will be most efficient for us.

If we fly out of the Southend London airport, any recommendations how we get there from London? We weren’t planning on renting a car, but maybe we will need to? Anything to see along the way?

This might make me re-think this option and go back to the train from London to Paris, then train to Bayeux.

I looked into flying from Southend last time I was over (but ended up using London City instead). There is a direct Greater Anglia train from Liverpool Street station to Southend Airport station, which is right in the airport.

As I said in my previous answer,

not especially well connected to London with the all-stops commuter trains going from Liverpool Street,

you take the tube, bus or walk to London Liverpool Street Station in the northeast of the City of London, quite close to the Bank of England and the Gherkin, and join one of the usually 12 coaches long commuter trains (usually stops at all 8 stops, every few minutes) to Southend Victoria and get off at Southend Airport 2 stops from the end of the line. The trip takes about an hour. There are normally 3 trains an hour.

All bets would be off today and tomorrow because all trains on that line have been cancelled incase it snows, but that is unusual. So look further out for details.