I was given a Bionx motor, battery and charger station from a friend who asked me to convert his KTM MTB into a regular bike. The KTM charger station used a bog standard 'PC' style power cable ending in a C13 connection. The device switches automatically from 110-250v, so for most of the world, it is just a case of having a suitable wall pug connecting to a C13 connection.
C13 are plentiful and inexpensive and should be easy to find via Amazon or Ebay in European/USA and other variations due to use on PCs, many monitors and other devices, and can probably be sourced with compatible wall socket plug for wherever you intend on travelling to. You could then just leave the UK cable at home and get one that meets the requirements of the country you want to travel to.
This assumes that your camp site has suitable power outlets available for you to use.
An alternative solution, and one I use when I travel to/from or receiving visitors from UK/Germany is a 4er UK extension cable where I cut off the UK plug end and replaced with an EU plug. So it fits securely in the German/EU standard wall sockets, but provides 4 UK outlets that can be used without extra adapters. And I made the same in reverse with a UK plug with 6 EU outlet extension cable for when I am in the UK and want to to the same with EU plug devices.
This is not the best idea if you are trying to save weight or space in your luggage- but otherwise offer a good sturdy alternative to adapter plugs.
BE AWARE that different countries have different rules that apply to E-bikes. In Germany, to ride without a licence plate, the bike as to be an electrically assisted cycle that only assists when pedaling at same time AND restricted to 25km with e-motor assisting it. Faster bikes, or ones which can be powered without pedaling, you need to have a number plate and special insurance. I don't know that there is an EU standard rule when you cross borders, but if you were involved in an accident with a bike that did not fulfill local regulations, you might end up in a heap of trouble and potentially be liable for costs for riding contrary to local laws even if you were not at fault in that accident.
Best would be to check with manufacture about the standards the model of e-bike you are interested in covers, and then research what are the requirements in the country you wish to travel to- to make sure if there any rules you need to follow for those standards.