Except that Apple Inc doesn't exist in their jurisdiction, and there are good reasons why it doesn't work that way.
Consider the possibility that they just not operate in the UK at all. They sell iPhones to a global retailer in the US, the independent retailer imports them into the UK and sells them to customers there. Apple sells exactly the same number of iPhones to exactly the same end customers, but now they're not subject to UK jurisdiction at all.
If that's all it takes to avoid the global "profit tax" then that is what would happen. But that makes no sense. There is no sense or benefit in making the global tax contingent on whether the final low margin retailer in your jurisdiction is a subsidiary or not.
But if you still want to impose the same kind of global tax even through an independent entity then you have to go all the way back through the whole supply chain or it can be trivially avoided again, at which point all you've basically done is reinvent VAT.
> or should we be dividing UK revenue by global revenue and demanding a tax on that percentage of global profit of Apple Inc?
This also doesn't work for another reason.
Suppose a company (not necessarily Apple) has two lines of business. One is high volume low margin manufacturing commodity hardware, the other is a high margin software development. The hardware business is responsible for most of their revenue but only a small fraction of their profits, because the margins are very low.
If they sell a lot of hardware but not a lot of software in the UK then your formula is unjustly allocating profits from the global software business to the UK where they sell mostly hardware, and then they would have the incentive to stop selling you hardware because the tax would be more than their actual margin on the hardware. But if you let them apportion profits accurately based on different lines of business then we're right back to them being able to shift them into whatever jurisdiction they like by engaging in high margin transactions in low tax jurisdictions.
There is no such thing as profit as distinct from revenue. All revenue is profit to somebody in the supply chain. If you want to tax profit throughout a supply chain, all you have to do is make sure that you only tax revenue exactly once and you're done. But that's still just VAT or sales tax. Pretending corporate income tax is something fundamentally different is just introducing exactly the sort of complexity that allows international corporations to avoid paying the same taxes that domestic corporations still have to pay.