“Spaghetti Bolognese” doesn’t exist. Some people would call it a ‘Britalian’ dish, a dish of Italian origin that has been adapted to the tastes of English people and thus renamed. However, it can be found in e.g. Germany and many other northern European countries like Sweden or Denmark as well. Calling it ‘Britalian’ could rightfully be considered unfair.
The only country where it curiously can’t be found is Italy. If you manage to spot it on a menu there, chances are you found a non-Italian restaurant (in defiance of any claims to the opposite this restaurant might make).