Planning day trip to Bletchley Park from London on Oct 21. Staying in Covent Garden. Figured out we should take tube to Euston Station to catch train to Bletchley. Will have Oyster cards. Is there any need to buy the train tickets ahead? There will be 4 of us, and I think the travel both ways will be off peak. I think I remember when going to the Harry Potter studios from Euston we used our Oyster cards and the additional amount for the train was subtracted. But maybe for a group of four a group ticket of some kind is better?
Appreciate your help, Londoners. I live in Atlanta, and there are only 2 train lines for the 6 million of us, so European trains are often puzzling.