I'm glad you mentioned stock prices.
Let's suppose you are an oil company, who buys, sells and owns oil, which is priced in dollars, all over the world. Or a pharmaceutical company. Your turnover and your profits are calculated in dollars. Yesterday your shares were a pound each. Today the value of the pound drops by 16% against the dollar. How many of todays new, shrunken, 84pence "pounds" are your shares now worth?
Shell RDSB
Now let's suppose you are a clothes and household goods retailer. Almost everything you buy is imported, and the price you pay your suppliers is based on their foreign currency. But everything you sell is priced in pounds, because all your shops are in the UK. Your customers savings and incomes are in pounds, and so are their household budgets. Today the value of the pound drops by 16% against the dollar. How many of todays new, shrunken, 84pence "pounds" do you have to pay your suppliers for their socks and washing machines? But how many of todays new, shrunken, 84pence "pounds" do your customers have in their pockets to pay for them? What happens to your share price?
This does:
Debenhams DEB
So if you look at the index, you will see winners and losers. Some of the gains and losses are directly and very obviously attributable to the Incredible Shrinking Pound, and/or the planned loss of access to the Single Market..
Now suppose that you are a housebuilder. Or a plumber. Or a recruitment agency. Your customers live in a country where their savings and income have lost 16% of their value, and where investment and employment are falling. How much money are they going to spend on new houses or bathrooms or growing their workforce?
Now suppose that you are a US vulture fund or investor. You see that the dollar price of some companies has fallen by 16%. You see that investors in, for example, shops and offices are scrambling to sell for whatever they can get. Do you snap up a few bargains?
Land Securities LAND
But if you are a UK person with a pension fund, what has happened to the value of your life's savings?