Lots of tactics for finding cheaper fares.
As Yorkie says, the clusters help.
It makes sense to check splits first, and then maximise distances using the clusters.
E.g, for your journey you've got
Redcar Central - Mayrport
http://brfares.com/#fares?orig=RCC&dest=MRY&rlc= &expert=on
£44 Anytime Return (undiscounted price)
And the actual route is:
Redcar Central - Newcastle
Newcastle - Carlisle
Carlisle - Maryport
Redcar Central - Newcastle is £15.40 return
http://brfares.com/#fares?orig=RCC&dest=NCL&rlc= &expert=on
Newcastle - Carlisle is £18 return
http://brfares.com/#fares?orig=NCL&dest=CAR&rlc= &expert=on
Carlisle - Maryport is £11.60 return
http://brfares.com/#fares?orig=CAR&dest=MRY&rlc= &expert=on
So that's £45 - no saving
Then trying to stick these segments together, you find
Redcar Central - Carlisle
http://brfares.com/#fares?orig=RCC&dest=CAR&rlc= &expert=on
£25.50
Carlisle - Maryport we know is £11.60
So that's down to £34.10
Trying the other two segment merge, Redcar - Newcastle at £15.40, then Newcastle - Maryport is £27.80
http://brfares.com/#fares?orig=NCL&dest=MRY&rlc= &expert=on
So that's £43.20
So splitting at Carlisle is clearly the best approach, although looking at the DAY return fares from Newcastle, it might not be if we were returning the same day.
Here the problem can arise of the train not stopping at the stretched point. So we do need to check.
For Redcar - Carlisle (£25.50), we see that we can actually stretch as far (check the map:
http://www.nationalrail.co.uk/passenger_services/maps/nationalrailnetworkmapZoom.pdf) as Wigton for the same price.
So Redcar - Wigton is also £25.50. A quick check on NRE shows that all trains Carlisle to Maryport call at Wigton. So that's no problem.
Wigton - Maryport has no day return fare
http://brfares.com/#fares?orig=WGT&dest=MRY&rlc= &expert=on
so we just buy two singles for £3.20 each
So that's £31.90.
Incidentally, if we check fares from Middlesborough, in the next cluster closer from Redcar, we see that they are the same to Wigton as from Redcar:
http://brfares.com/#fares?orig=MBR&dest=WGT&rlc= &expert=on
So we are getting good value from Redcar.
In this case there's just one TOC, but in cases where the are several TOCs on your route you can find that playing on fare competition by splitting between stations that have competition can help, and simply splitting so one section is all on TOC A and the rest all on TOC B can also work.