Rule #1 of buying silver in the UK - VAT really ganks the value of investment in silver. Buying and selling through conventional dealers will get you a spread of 30% or more, which makes it not worth doing this way.
But . . .
You can buy and sell on the secondary market at manageable spreads. If you keep an eye out here and the various other places where folks buy and sell silver, you can buy and sell at a far more sane spread. The going rate for 1oz coins is somewhere about £23 (give or take - maybe a little more with silver going up), and there are people you can buy from around this price point. Bars in the 10 oz to 1kg range are also worth buying at the right price.
You need to understand your exit strategy, which is just a fancy way of saying 'How do I flog my coins?' With silver, buying and selling to dealers isn't cost effective, so your exit strategy for silver will have to be based off selling back to the secondary market. Therefore you have to pay attention to liquidity - i.e. what people will buy, and at what price you can make a quick sale. As a starting point, think of tubes of 1oz coins, and bars in the 10 oz to 1kg range. Take a look in the UK ungraded section for sales to get a sense of the going rate for these on the open market.
Consider also buying gold in the portfolio, unless you really want to bet on silver going to the moon. The folks in that video are notorious for circulating clickbait about how silver is about to jump in price, and have been running this schtick for years now.