London to Bayeux

either train all the way (via Paris) or ferry across the Channel

more info here on how to book https://www.seat61.com/France.htm#London%20to%20Normandy

We specifically went to Bayeux as an intermediate on a trip that started in London and then went to Belgium and Amsterdam.

We took an AM Eurostar from London to Paris, very inexpensive when booked months ahead, and then walked from Gare Nord to St Lazare and took the direct rain to Bayeux, also inexpensive, booked in advance, about a 2'10" trip. We walked between the stations as to take the Paris Metro would have meant walking over 1/3 that distance anyway. Took about 25-30 minutes. Disclaimer, when we did this we were both just past age 60 and carried our stuff on our backs in the RS Convertibles. Realize this might not work for all.

Have you already booked your flights? If not, then you might consider flying open jaw/multi destination in to London and out of Paris or vice versa, that way you don't have to backtrack for your departure flight.

If you are going to include the DDay beaches in your Bayeaux trip, I'd suggest at least 2 nights in the area so you have 1 full day.

Thanks. Excellent advice.

We started our trip to Bayeux by taking a cab from Heathrow to St. Pancras to catch the Eurostar to Paris Gare du Nord, followed by a stressful wait in the cab queue at Gare du Nord for a cab to take us to Gare St. Lazare, and finally taking a train to our final destination of Bayeux. Luckily, all the pieces of our Runyanesque plan fit together nicely on that one day.

All of this was necessary because we couldn't get a flight to Paris using reward miles when we wanted to go. I wouldn't recommend this approach, but our three full days of D-Day tours, plus the Bayeux Cathedral and Tapestry, were totally worth it.

The Tapestry is amazing.
Be sure and read the book 1066, which explained the story of each panel of the tapestry.