"Copying one source is plagiarism. Copying more than one is research "
Another rich source of information is TV Times, from the days when it was a TV magazine, and not attempting to replicate Woman's Own. The first few years are particularly interesting, as they contain articles written by many of the pioneers, such as Norman Collins, and include details of their operations and transmission maps. The viewers' opinion can also be determined from the letters page, some critical but most are, as you might expect fulsome praise.
Less reliable are the autobiographies of those involved, such as Lew Grade and Howard Thomas. These were written years after the event and don't always square up accurately with things such as dates, but they do offer personal insight. For a general account of the whole development I would still recommend Peter Black's Mirror In the Corner, even though it is now 25 years old and sometimes difficult to get hold of.
The copy of the Annan Report which I purchased for 10p in a sale from Dorset County Library was well worth the money.