Essentially, if you asked whoever runs the country what gave them the right to force people to do things against their will (ie, to make and have enforced the law), they would have a valid claim to power if their response made you say 'OK, fair enough'. Since we generally view government as a social contract nowadays - that is, the state has the right to power over people because those people, by enjoying its protection and the benefits of living there, implicitly accept that as part of the deal - the only truly valid claim to power is the consent of the governed.
This can be active consent ('80% of them voted for me as President') or tacit consent ('nobody ever protests against the monarchy, so they must support it') - most would say that the latter needs some element of the former as well. The current situation in this country is a bit complicated, but in 1997 we could say that the Labour Party had the active consent of the people because a majority of them voted for his MPs, and Blair had their tacit consent because everybody knew that the leader of the largest party would be appointed PM, and nobody complained about that.
This can be active consent ('80% of them voted for me as President') or tacit consent ('nobody ever protests against the monarchy, so they must support it') - most would say that the latter needs some element of the former as well. The current situation in this country is a bit complicated, but in 1997 we could say that the Labour Party had the active consent of the people because a majority of them voted for his MPs, and Blair had their tacit consent because everybody knew that the leader of the largest party would be appointed PM, and nobody complained about that.