Nice to hear you're interested in Commanders! I lived in UK for many years and flew there quite a bit. Never any twins. But the place would be perfect for them with all those short grass strips. I used to fly into Damyns Hall, Denham and Elstree all the time. All three would be a piece of cake for a light Twin Commander.
What lead me to Commanders was the utility factor. I've always liked the idea of being independent in my flying and being able to get into airfields that are either challenging or short and without ground support. I also like high wings and a good view. And the Commanders are great at all those things. They're equally at home on a bush strip in the Andes, as they are taxiing up to fancy FBO. It's the Cadillac Escalade of the sky.
As for why it need to be a twin, well, today, I simply don't feel safe in singles. I know statistically that might not be the case, but in a twin, when one quits, you normally don't end up as a statistic. In a single, you probably do. And especially in the UK where every flight abroad is either over the Channel or the Irish Sea, it's good to have that second one purring out there. Long stretches over water at winter or at night - I don't know how the guys do it in singles. I'd be a nervous wreck.
You should go and have a look a G-AWOE at Elstree. I believe it's still for sale. It's a 680E with the geared engines. They're supercharged, so won't be able to do Mogas in them and it's high time. It's been sitting for quite some time since the owner died (he used to own Elstree Airfield), so might be too far gone by now, but at least you could get a feel for it. The geared Commanders will always have shorter takeoff than then non-geared. They just have more torque and will get going quicker. My 520 was insane in that regard, as you can see in some of my videos. But a 560F will do almost as well, and it's a bigger plane with greater range. But geared engines will cost more at overhaul and to keep running, so it's a balance one has to make.
Otherwise, the safest bet is to buy a 500A or B model. They're great planes with straightforward systems. They won't takeoff quite as short as the geared ones, but they're still pretty good. A 500B is just bulletproof and a gold standard in Commanders. And in Europe, you'd want a model like that that's easily worked on, rather than perhaps a geared engine that very few can overhaul or support.
Let us know how it goes.