The border agents at HMRC will suffer quite a loss of sense of humour if they decide to check whether you paid duty on that giant Apple device you are carrying through the green channel on arrival from the UAE (at best they'll delay you for some time and if you confess, you'll have to pay the VAT and a penalty). Since this is not something you could claim is under the taxfree value limit nor is it something you can conceal in your bag, I don't recommend it. I don't actually recommend such VAT/Duty fraud at all; I'm actually doing quite well on declaring such items as camera lenses and being waved through with no duty to pay, yet above the law

Perhaps just resign yourself to carrying it on your journey?