Re: Go right ahead...
That's like saying if you raise income tax everyone will emigrate. Only if you do something INCREDIBLY stupid and price the company out of the market. A £3bn company isn't going to disappear overnight even if it wanted to and certainly isn't going to stop selling licenses until it *costs* them money to supply them. You would literally be looking at something like 70-80% tax on profit before that happens (remember, it's a tax on PROFIT).
Additionally, if Oracle has to leave the UK because it can't afford to operate... FABULOUS. There'll be a humungous rush for the database market in the UK that doesn't involve them, and lots of other companies will make SOME money (maybe not on the same scale as Oracle did) and we'll pay less for database licensing. Same for Symantec. Same for Xerox. Same for Dell. Same for just about any company.
These companies are doing nothing against the law. Which, in effect, means the law is broken because being able to say you made zero profit in the UK because you paid YOURSELF in another country all the profit, is a blatant tax loophole. Just because it's legal, doesn't mean it's right, or that it should be legal tomorrow.
You could enforce corporate tax on those profits, and tax them to 50%. It'll change the market, but there won't be a mass exodus. If anything, it'll only make things better - you and I will have more money or pay less tax (because the government doesn't need to make up that shortfall any more from our income tax), and those industries will have more competition.
Hell, it might even boost open-source take-up and force government procurement to use suppliers that are more suitable. But that's probably just a pipedream.