Prepping/SHTF wise: I think your generally better off spending the money on food ect, every time. People will say precious metals are a guard against economic meltdown, but realistically they’ll only take you as far as the collapse of fiat currency. You’re still totally reliant on being able to spend you gold or silver after the fact. So I believe in cutting out the middle man and getting the stuff now while it’s still for sale. As for having a bit of silver on the side to use in barter, that’s different. Although again I can think of many things I’d rather spend my money on. £100 would probably buy you 1000 disposable lighters or just over 4 ounces of silver. I know which I’d rather have to trade with after a collapse.
As an investment: that’s not really my area, and clearly some people will have done well out of the skyrocketing prices we’ve seen. Then again though in order to do really well you’d either have to plough some serious money in, or pray for another massive increase. I mean if I’d bought a grands worth of silver a few years ago I’d have doubled my money, would have been a nice little windfall but nothing spectacular. One the other hand when I was I started uni in 2008, I was really tempted to take that maximum £15k loan your allowed and put it all into gold, cash it in after I graduated, but I bottled it......that I regret...
If you do want some though, I think what Ian said is a pretty good place to start. I also remember eBay had some real bargains a few years ago but last time I checked the going wasn’t so good.