The issues are simple....
1) We can easily switch off FM and have a digital radio service.
BUT....the replacement, whether it is the current DAB system or a better (DAB+?) system, must be properly thought through....as things stand right now, over 10 years AFTER the launch of DAB, is that some area's still don't have ANY reception.
This needs to change.....we need 100% coverage of digital radio, BEFORE any decision to shut down FM.
2) Currently, the DAB frequencies are allocated by OFCOM, who have chosen to only licence a few....
So, to kick off then, we need a wider range of frequencies (ie multiplexes) to be licensed immediately, so that existing DAB stations can broadcast at higher bit rates and hence we can have quality digital radio (coz DAB at 192kb sounds pretty good!), rather than pi**-poor 128 kb (or less), which sounds awful.
3) With more multiplexes available, every local BBC radio station can be heard of DAB, in their local area.
Get these up and running and then local commercial operators will move across from FM, once more people listen to the BBC on DAB.
The driving force for uptake of DAB has always been the BBC, so get them behind on a local basis and the rest will follow....
4) The entire DAB network mainly uses the old 405 TV transmitters....so, we need OFCOM to pressure Arqiva to ensure that each of these, including the relays, are all fully operational and running at the right power levels to provide 100% coverage as in point 1).
Only after all the above are sorted, should we think about switching off FM.....but as you can see, to do the above wouldn't take long as the infrastructure is already there....!
Job done.