Question

Why was the government of britain an oligarchy rather than democracy

Answer 1

Firstly, I would say that for sure, during the medieval times, it was an oligarchy ruled by the aristocracy ie by a small minority of rich and priviledged nobles. Now, though nominally Britain is a democracy with elections, in fact very low numbers of people vote, like only 30% so in fact it tends to be the elites who get into power without a strong mandate from the people and implement policies as they see fit, most like as a neoliberal type government that defends the rich corporations against the interests of the broad masses of the people. 

Answer 2

Taking in consideration the question is necessary define in few words the concepts of Oligarchy and Democracy.

According the Encyclopaedia Britannica Oligarchy government by the few, specially despotic power exercised by a small and privileged group for corrupt or selfish purposes.

And Democracy is a state of society characterized by formal equality of rights and privileges.

I think that the government of britain was an oligarchy rather than democracy, because its central of power was the imperial and in that context the only system of government possible is Oligarchy.