The Conservatives in Totnes selected their candidate for the Westminster election via an American style primary election. A primary election is very similar to our hustings where party members get together to select the party's candidate. In America there are two types of primaries, open and closed primaries. In the closed primaries only those people registered as Republican and Democrats can vote in their respective primaries. In the open primaries registered Democrats can vote in Republican primaries and vice versa, which is the process used in Totnes where all registered electors had a vote. The open primary is open to all sorts of abuse and manipulation by the opposition parties. I recall a few years ago that an open primary in Mississippi was subject to a court challenge because white Republicans were voting en masse against Democrats's strongest challenger and selecting the weakest candidate so as to giver the Republicans a better chance of winning the seat in the subsequent General Election.
I'm not saying this happened in Totnes but it most certainly has the potential to happen if the opposition parties ever succeed in getting their act together.
UPDATE - This is the case in Mississippi