Yes, i often chose to go via london to travel to the North. In 2004, it was cheaper to go to leeds from Swansea using FC Advance fares than it was on an XC priced Advance via Brum!
In the days of Virgin, I was planning a trip to newcastle, and being without a PC at the time, I rang Virgin telesales. The guy advised me to split the tickets at Bristol Parkway to get the cost down!
What I was really getting at though, was the well known split at Cheltenham Spa trick for South West passengers, who can save a packet on the through fares from places like Plymouth to Birmingham and points north. As the fares to Cheltenham are priced by FGW, most of the trip is udnertaken on a cheaper ticket, and as all trains stop there anyway, one can travel throughout on a through train without paying XC's silly prices!
I think this is where their business plan has come unstuck! Add in people finding ways around their afternoon restrictions as well, and we can see how revenue is lower than forecast and yet the trains are still rammed on the central sections. You can just imagine the bean counters rubbing their hands with glee as they put in their franchise bid:
'Oh look, we can extract 27& more revenue on these flows, 35% more on this one, the tight wads will go by coach and there won;t be so much overcrowding, of course we will be able to afford the bid'
Unfortunately, their knowledge of rail ticketing was simply not good enough! And apart from the split I've quoted, there must be many more in other parts of the country!