In Frank Leavers Sunday Politics article, Frank suggests the leader of the opposition party role is essentially to hold the government to account and in doing so, is central to British democracy.
Unfortunately that view was held by many members of Parliament who were voted out of office by the British electorate for going against the democratic vote of the people to leave the EU. They thought they knew better than their constituents and rightly payed the price.
It is not the opposition party or any other party to go against the will of the people. Hence the opposition parties disastrous thrashing in the recent election. British democracy is in the hands of the people who vote, not politicians of the day.