Going by what you say above my nephews are doing quite well then with the Britannias, that is good to know.  Apart from that single exception I was never tempted by new issues at all.

I started hoarding coins when we went decimal, just keeping what I could in date runs before they went out of circulation.  Then I started buying the ones I was missing (this was back in the days when it was economic for a retired gentleman to have a kiosk in my local station).  I realised that I needed to specialise when the collection got too heavy to carry easily. 

I traded in all the copper and most of the silver to Coincraft in London and my collection became pre-decimal silver, first year of issue, one uncirculated example of each.  I still have that collection but have gone as far as I can go with it.  The lower denomination Young Head Victorian and William IV I could afford but half-crowns and crowns are out of my price range.  If I remember correctly the plain head Victorias cost about £5000 and £10,000 each and the Gothic issues even more (and that must have been at least ten years ago).

I can see what you're saying about protecting savings especially with interest rates so low but aren't there some drawbacks as well?  For example, you won't get a Britannia for £14, there is the Mint mark up and if you buy through a third party they want a bit too.  The same would apply if you sell, bullion dealers would offer less than the spot price.  I'm sure you know what you're doing but surely bullion prices go down as well as up, just like every other form of investment.  Many other people are doing the same as you, so some of the higher price is because that is inflating the price.  I would be a bit worried that I was buying into an inflating bubble.