The United Kingdom Competition & Markets Authority has been rethinking how competition in passenger-rail access can be improved. They have just issued a preliminary report with four options, and are soliciting public commments up to October.

I suspect the discussion, and perhaps the option(s) ultimately chosen, will have an impact on preservation rail operations.

Link to the downloadable (PDF) reports and supporting material is here:

https://www.gov.uk/cma-cases/passenger-rail-services-competition-policy-project

Actually I think the very little if almost nothing to do with heratige operations on the main line railways but with how day to day operations are conducted and offered to the riding public.

The only effect I can see on heritage operations (both steam and diesel) on the main line is the possible reduction in available train paths due to the increased number of trains that may operate through the hoped for competition. It is becoming increasingly difficult to find spaces at the moment on some lines, so this will just accelerate the process.
The fixed track access payments, if applied to specials, however, may have a big effect on the fares payable on such trips, as they will have to be passed on to the customers!

The C&MA have raised this idea before and got short shrift if only for the reason that permitting some form of level playing field on most routes would involve taking allocated paths from franchised operators.

At this time the UK Government (Department for Transport) have their hands full in dealing with the current and potential massive fall out from Network Rail's inability to control costs of current improvements (electrification), lagging behind in track/signalling maintenance and improvements and seeming inability to reach first base in planning currently authorised electrification (Trans-Pennine and Midland main line).

On rail competition on the same route struggles to work at all. The regulator, in attempting to find paths for potential open access operators on the East Coast main line will probably have to "adjust" future planned timings for the present franchisee (Virgin East Coast). If this happens it will probably bring forward a claim against the government by them.

Regarding steam/diesel heritage operation on main lines, it is already being anticipated that in the not too far distant future such trains will no longer operate from major London termini and be limited to lesser used routes in the provinces such as Hellifield - Carlisle, Chester - Shrewsbury - Newport, Chester - Holyhead reverting to what British Rail permitted between the late seventies to the mid nineties.

Isn't the real issue on the delay of electrification on the Great Western, where the delay will prevent the full use of the dual powered, very expensive, Intercity Express trains (the internal combustion side of these trains are too underpowered allow them to reach their full potential performance), that are intended to replace the aging HSTs?

Are there really that few paths available on weekends, when most of the specials operate, to force them out of the London Terminals?

The document states that none of the changes being considered would take place until a current franchise is expired so no worries about taking paths away from the incumbent.

Unbelievable with these issues, and the British railway press basicly calling Network Rail incompetent after the post Christmas Kings Cross and Paddington meltdowns, that California High Speed would hire them as consultants!