Calculating Train Fares -England

What you are looking at is often called "split-ticketing" and is perfectly legitimate, providing you are observing the rules of tickets that may be limited to a certain operator, and the train stops at the split point (even that isn't always necessary but that requires yet another level of explanation).

These arise mainly because of the differential treatment historically and sometimes more recently of tickets confined to one area, length of journey or set by specific operators. Here it is possibly significant that both Gatwick and Peterborough were in the old Network South East area but Stamford was not but it could be something else.

Some websites can work out splits and thereby offer cheaper fares although they often take a cut of the saving.

The pricing of rail fares in Britain is crazy. Try using this site as it will tell you if splits will be the way to go:> https://www.trainsplit.com

Where it says ‘Proceed’ - click it - (you are not committing to buy yet) & it will tell you the prices and where the splits (if any) occur.

Look at three tickets:

Gatwick to St Pancras = Anytime £12.10

Kings Cross to Peterborough = Advance ticket from £12.50

Peterborough to Stamford = Anytime £8.55

Oh wow. Thanks so much all! I couldn’t figure out what was going on. That helps a lot

You must pre-book Advance tickets - the others you can buy on the day at the station giving you more flexibility.

The man in Seat 61 recommends loco2.com and I concur. They will split the tickets for you. No booking fee.

I explained that in your previous post https://community.ricksteves.com/travel-forum/england/britrail-pass-london-or-england , the second answer.