Actually it's a little more nuanced than that. If you buy an activation locked MacBook from a registered business in the UK and have an authentic receipt for it

Actually it's a little more nuanced than that. If you buy an activation locked MacBook from a registered business in the UK and have an authentic receipt for it, Apple will unlock it. I know someone who has been through that process. If the device is marked in lost in iCloud though, it isn't happening. Ergo if you're going to risk it, stick it on a credit card.