After the switchover I believe some relay transmitters were switched off therefore the aerial maybe pointing in the wrong direction.

Yes, silly me, signals are stronger. Wondered whether they are overwhelming aerial booster. Prob not! Must have something to with my aerial and its orientation; will continue playing.

Yes, my home TV gets much better reception now from CP on its roof aerial.

OK, I've now tuned all 113 stations on Hannington (South) transmitter. It turned out that I had to change the direction of my aerial thro' 90 deg, altho' Hannington hasn't moved. Perhaps, as you suggest, a relay was taken out, altho' I thought I was pointing at the strongest signal.

I had to massage the tuning data of my TV tuner programs, cuz the muliplex channels and frequencies had changed over the switchover. Indeed a couple of the frequencies on the official Freeview site for Hannington were slightly out (by 0.2 MHz) sufficient for one of the TV tuner programs to skip over them until I amended them based on data from the other TV tuner program.

As regards the OP, I have no experience of WMC but perhaps its tuning data has run into the same problem.

I can now only get BBC channels

Which Area/Transmitter?

That's what I got before I corrected the frequencies.