They say they use foreign debt collection agencies to collect penalty fares.
I expect that relies entirely on whether each country’s car+driver registration agency supports the dishing out of owner details to debt collectors like DVLA does in UK for parking scam companies.
I imagine that Germany does not willingly give out such information.
But at £1.66 per crossing, doing it legit probably makes sense. But you have to load up the account with £10 or £20, I understand. No idea if you can ever get the remainder back if you close the a/c.
I’d probably stick my plates on my parents’ or brother’s a/c should I need to go that way. Although more likely it’d be a rental car from London City airport (so god knows how that’s going to work), and just use the other tunnel or Woolwich ferry for free.