Nicholas, sadly that is legal. In europe one only needs 12 hours of rest after a flight duty when at their homebase if duty was less than 12 hours. Downroute in a hotel it is only 10 hours if the preceding duty was less than 10 hours. Which allows some quite atrocious rostering patterns.
Anyway, before a longhaul flight in my company we have at least 16 hours of rest and the duty before that cannot be longer than 10 hours. However that is only a company rule, legal is as i outlined above.