A 1.8/9t with a full counterweight. Anything smaller will be severely compromised with the weight and build height. Maybe a direct mount on a 1.8t zero tail would work too.
Spec the right size buckets too, a lot of people overlook this but buckets can make or break a tilty setup especially at the smaller end of the market.
What he said.
Make sure you spec short dipper too- this is very important as all UK standard specs are silly long dippers. I run an E19 with top hitch and a tilty, short dipper and four pipes so no control system needed. You simply don't need a control system on such a small digger- keep it cheap. Mine has been a fantastic asset on the 1.9t- I didn't think it would be that good, and bought the tilty mainly for the 2.7t. But I've been greatly surprised how much easier it has made things on the 1.9t.
If I were buying again I'd probably look at a compact radius machine with additional counterweights. That way if access was really tight, you could remove the extra counterweight and just accept that it would be noddy for that job. Worked well on my old Hyundai.
I'd certainly keep the top hitch though. Extra power when bulking or ripping (and little machines need all they can get). Plus then you can run a breaker too.
if you fancy a bit of a trek to just over the West Sussex border you'd be welcome to have a play on mine.