I calculated, for a different thread, a rough and ready comparison between BR and the privatised railway in terms of number of vehicles delivered in two comparable periods. In the period 2000-2010 the privatised railway delivered 1114 DMU vehicles. Of those 495 were of the
22x family, 140 were of the
Coradia family and 153 were of the
Desiro family. I'd suggest those vehicles are not really appropriate for replacing Sprinters or lightweight Pacers. Meaning of those 1114 about 788 aren't really useful if our aim to is to replace Pacers and the lower numbered Sprinters (the remainder are of the 17x and 168 family's plus two PPMs).
Just for the sake of completeness BR between 1980 and 1990 delivered 1069 DMU vehicles of which 338 were Pacers and 588 were 150s/155s/156s. Meaning 926 of the 1069 were what you'd call basic and suitable local stopping services.
Privatisation has been very good at delivering new trains. It has been terrible, however, at getting new fleets of basic DMUs. For example in 2006 we had 185s replacing 158s that were barely fifteen years old whilst Pacers that were approaching twenty (and were woefully in adequate for passenger loadings let alone passenger comfort) had no replacement in sight. Building something that is basic and a good fit for the replacement of 14x and 150-156 is not something we seem to be good at.
It seems the best we can hope for is getting sufficient new (or cascaded stock) to allow 150s and 156s to be released onto those local stopping services.