Yes, in Europe breakers are rated for continuous load and there isn't a 20% de-rating rule (we have a 'diversity' calculation for if the load is less than continuous, so everything comes out much the same but things are just labelled differently). So the HPWC on 20A setting will draw 20A and that's OK on a 20A circuit. That circuit can't be shared with anything else however - if you've got for example a 20A circuit feeding your garage with lights etc. in there as well as the UMC, the maximum you could have for the UMC would be 16A.
When charging at very low currents, there's an extra factor in the calculation given above: the car uses a certain amount of power just to be "on" and ready to charge - as a rule of thumb, about 1A is 'wasted' hence the step up from 10A (UMC on domestic 13A socket) to 20A on the UMC will be a bit better than double - more like 19/9 = 2.1 times as fast.