Entente aggression and Belgian neutrality

What would Britain have done if France or Russia had been the aggressor in the First World War?

The Entente was an agreement rather than a binding defensive alliance, so British support would have been doubtful beyond action to secure Belgian neutrality.

Domestic opposition in Britain would have made automatic intervention for an aggressive France or Russia difficult. The Entente Cordiale created an understanding rather than a defensive treaty that mechanically compelled Britain to support either partner. Belgian neutrality was the clearer British security interest because control of Belgium could open an invasion route toward Britain. The answer corrects the common mistake of treating the prewar Entente as equivalent to a compulsory alliance.