We need a ballot line system, so that voters would be able to indicate that they were voting for a given candidate specifically as endorsed by a smaller party or other campaigning organisation.
Those organisations might be trade unions, co-operatives, peace and disarmament movements, civil liberties groups, or environmental campaigns.
Or they might be fighting for Crown and Commonwealth, for national sovereignty, for the countryside, for traditional family life, for the Armed Forces, or against expensive and socially disruptive wars with no British strategic interest at stake.
Among numerous other possibilities.
The number of votes by ballot line would be recorded and published separately. If a candidate owed either success or failure to a particular campaigning organisation, whether national or local, then he would know it.
And so would everyone else.