Most of the stuff you buy comes from Europe - Luxembourg, I believe. That's certainly where everything I've bought from Amazin came from.
They can very easily cease to employ and pay ****loads of UK staff. Let's not forget that we are talking about some of the very largest and wealthiest corporations on the planet - truly global businesses. It's nothing for them to relocate if you make the business environment unfriendly.
These guys run businesses that are not only truly global, but completely transient. Yes, it's convenient for them to operate from the UK - at the moment - but as alluded to earlier, even that may change with the Brexit vote.
It's an increasingly competitive world we live in. The U.K. Must compete business wise, or die! Living in the 1970's, as Corbyn and his allies seem determined to do, will destroy what's left of the economy in the UK.