All joking aside, that is not even funny and totally shocking and potentially lethal. I'd be storming back into the dealership and speaking to the principle to a) ensure this never happens again and b) that the tech involved is "re-educated".
If (god forbid), you went to use the wipers in a sudden downpour and could n't see where you were going and crashed and either injured yourself or worse someone else - then the dealership and VW UK would leave them side wide open to be sued to the fullest extent that the law allows !
I agree that's a shocking error (but not quite as bad as a Ford dealership who serviced my XR3i and forgot to tighten up a brake valve, as I discovered at 70mph on a dual carriageway!).
However, I'm sure the police would tell you it's the
driver's responsibility to ensure that the car is fully operational and safe
before it is driven on a public highway. You could try suing the dealership but legally you would be responsible for any accident.