Well, we had promised to protect Belgian neutrality. (And not through any great sense of altruism: it had been long-standing British, and before that English, foreign policy to disrupt continental powers seeking to strengthen their presence on the north-west European coast, going back at least as far as Elizabeth I’s support of the Dutch in their war of independence against Spain; I think Richard III took some time out from murdering the Princes in the Tower for an expedition in Brittany on similar grounds.)
