Others, like the 2.2Kw Axminster ADE4000 Dust Extractor
don't have soft start. Axminster have told me that I
should double the running current and add another 15%
in cold weather.

Your design current doesn't include startup currents. You want to use Type B
if at all possible, as they are safer. These can accept a startup current up
to 3 times the design current, which would appear to be fine, as your worst
case scenario is the 2.2kW at x2.3 current which will give 22A which is not
going to trouble the wiring or a 32A Type B MCB, even if the ring is already
nominally fully loaded, unless the startup current lasts for an unduly long
period of time.

Christian.