US citizen to UK for 2-4 months personal tourism: Issues with a couple of expensive personal computers?

I'm considering/planning an extended personal visit to the UK for tourism purposes, with spouse. 2-4 months, on a standard "non visa" arrangement. Goal is to live in a rented apartment while spending much/most of the time seeing interesting things in London and throughout the country.

But lovely as the place is, with museums, stately country homes, cathedrals, remnants of Roman and earlier peoples, beautiful country, places to walk, ice cream shops, etc., I can't spent all of my time seeing sights. (My wife can, but not me.) So I'm bringing along other stuff to do. In fact, for me it will be like a busman's holiday: I'm a programmer, and I also program for fun.

So I want to bring two high-end professional "workstation" laptops, my standard development environment, strictly for personal purposes. Not-for-income programming. I mean, don't we all do that? Sure we do.

One is relatively recent, the other not, and they will be going back to the US with me, pos-def. But they are still high-end, and, there are two of them. (I know from experience I can bring one such machine with no problem. But two seems like it might be mistaken for something for work. Especially since I am, in fact, a software "engineer", and generally working for my own business, at that.)

So: Can I just bring them? Is this a job for a Carnet? (Why isn't there a Carnet tag, BTW?) Or, is something else involved?