After the Trading, Profit and Loss account, the profit shown attracts corporation tax. Something's are not allowed, eg. depreciation (so that's added back on), and if buy an asset, you will want to use the tax relief on it (known as deferred taxation). So corporation tax is then calculated. I'm limited company, so say after corporation tax, it leaves £30,000. I can take up to that £30,000 as a dividend. I don't pay tax on that because it suffered corporation tax
Now, if I invest in the business, some of it might be in repairs and renewals (repaired a building but upgraded it slightly, then the purchase of new assets. But my accountancy days stemmed from 1985 to 1989, so I'm not up to date on how large companies have to show their accounts.
If there was a straightforward way to say, "A company must invest % of bla bla", it's certainly not as straightforward as you're imagining things. And it's worked like that under every government for decades upon decades.
I believe media companies can no longer be bought by foreign countries. I would be the first to say UK companies should be wholly UK owned, sadly, global business does not work like that. If you or your mates are not willing to buy your water company, but the money comes in from abroad, then that's how it goes.
Do you thing if Starmer gets in he pushes a law through banning foreign countries investing in the UK? I doubt it. So now what?