Hi all,
I carry a polarity tester similar to hymer524's suggestion.
I also have a basket load of leads some inherited from my dad who toured the continent for 40+ years.
these include
the normal hook ups, one 10 metre and one 15 metre, (25 total)
a household 13amp plug to blue site connector
a household 13amp female socket to blue site connector
a reversed polarity hookup adaptor
an older shuko to modern blue connector
an older shuko to reversed polarity modern blue connector
A bit OCD but everything covered
Davy