Re: an easy fix to this situation
"So really there is no easy fix - multinationals will always need to sell things internally and there is nothing anyone can do to change that. (not saying its fair, just pointing out the facts)"
Yes there is an easy fix for transfer pricing. It is already the case that unfair transfer pricing is illegal in the UK(and most other jurisdictions). And under OECD guidelines HMRC can already recalculate companies profits where they believe that transfer pricing abuse has occurred. BUT THEY CAN'T BE BOTHERED.
They'd much rather hassle you and me to submit our poxy self assessment returns, even when we pay under PAYE, and then they'll hound the laggards with oppressive fines that no private company would be allowed to exact for late documentation.
So in the example you give, if HMRC would do the job they are paid for, Dell would get a bill based on the profits to be made buying at the the going rate for commodity laptops, and that would mean that they potentially pay tax twice, here in the UK, and in the Netherlands.
So the simple solution is to get HMRC's top management in to a room, tell them their employment will be terminated if in twelve months they haven't made serious inroads to the abuse of transfer pricing. Maybe the tax dodgers will try and find new loopholes, but HMRC should make it clear to business that they are in the long game for whack a mole, and threaten retrospective tax rules if business play silly beggars. In the meanwhile, dramatically simplify the UK tax code, to eliminate loopholes.
None of that is beyond the wit of man, but it may be beyond the wit of politicians.