OK, I know the UK is a free for all in Class G (VFR or IFR, nobody cares), and it sounds like the real answer to my Q is that people don't operate those types under IFR in Europe outside the UK.
With a 20k ceiling, my TB20 has a much greater IFR mission capability than a Trilander yet I would scrap many flights into other parts of Europe because I would be in solid IMC, heavy turbulence, and collecting ice for several hours. The Trilander has rubber boots but they would run out of sickbags if they were doing this.
Presumably the Jersey run is scud run below the TCU/CB bases if the weather is bad.