Ok..............................
If you send an item 1st or 2nd Class and do not pay for extras you aren't covered for anything, you have absolutely no right to claim, not a bean!
Proof of postage is a reciept that you request from the Post Master when you mail your item, this is basically a till reciept you can show the sender but is in no way a document which you can use against Royal Mail to claim for any loss.
If you pay 64p to have your item Recorded, the reciepient is required to sign for the item and you are then insured at the lowest level for any losses, you can claim a maximum of £28, this process takes about four weeks. However, you can insure your item for an additional £100 at the cost of 42p, but most people decline this service!
The best way to mail out your items are Special Delivery, if you use this service your item is guaranteed to arrive the next day before noon, if it doesn't arrive before this time and is late you get your postage cost refunded, it also insures your item for £500 automatically and you can choose to pay a little extra (can't remember the price off the top of my head) and insure your item in two other price bands £1000 and £1500. Special Delivery items are kept seperate throughout their journey within the postal system, they travel through a Priority Services channel, this is highly effecient and very, very secure, I cannot promote this service enough, it's actually a Royal Mail product that works, the only downside is that it's a little expensive, rates start at £3.65, but it really is worth it!
Hope this helps!
TC.