I heard quite a few had to pay postage on their own letters! Maybe the youth in HR don't know how to use stamps!
Whenever I have been involved in redundancies, fortunately not often, the letters have had to be sent out by recorded delivery or registered post so that it can be proved that the notice had been served. If the letter is lost on the post then I think I am correct in saying legally it has never been served and any dismissal would be deemed to be automatically an unfair dismissal by any tribunal. This might be something the unions can advise on.