Competition concerns were raised when First gained the SWR franchise, because of overlaps with GWR, particularly London - Exeter and London & Salisbury - Bath & Bristol.
Nothing came of it, as long as there was no occurrence of price fixing.
True - we get this every time a franchise changes hands, people finding examples of flows where there's a new "monopoly".
Stagecoach were fine to run the three InterCity franchises north of London - the only bit that the competition people found to complain about was the minor overlap between Grantham and Newark IIRC (since they also ran buses in this area - part of the old Lincolnshire Roadcar) - but fine to run all the daytime trains from London to Edinburgh/ Glasgow!
Fine for franchises to be merged together (e.g. Anglia + First Great Eastern... Valley Lines + Wales & Borders)... fine for one mega franchise in south London (Thameslink + Southern + Gatwick Express)... we had arguments when Arriva had the Wales & Borders franchise plus the Northern one... we'll be having the same arguments next time the Government actually get around to awarding a new franchise too.
I mean, the TPE WCML services are going to be operationally separate from the rest of the franchise, with dedicated stock (the 397s), so it *could* be split off much easier than a few years ago (when the "Scottish" services were interworked (and even portioned) with the Windermere/ Barrow/ Blackpool - Manchester Airport services - but it's only a few days since we were discussing improved co-ordination north of Preston (and why can't the operators work together to improve capacity/co-ordination during the Edinburgh Festival...)