Thank you Neil.
As I hoped, my statement on this forum resulted in an immediate response – something I was not getting recently by using the normal channels. It also resulted, after two days, in the required back numbers arriving by special post. On the same day, five weeks after I paid for them, an envelope containing one or other of the original sets of three magazines also arrived!
All I asked of the person on the phone when the first set hadn't arrived was that replacements could be sent by first class post, but I was told categorically that replacements would take yet another 7 to 10 days. Not the best way to deal with a frustrated customer, and obviously not the case!
John