In this scenario there is an organisation (UK based) with certain governing powers/responsibilities for a particular geographical area. There are a number of elected representatives responsible for decision making within that organisation.
Representatives are elected in a first past the post system, with one representative elected from each sub-region within the area. A number of the representatives are members of political parties and one of those parties currently holds a majority of seats. There are 4 opposition parties.
In this "hypothetical" scenario, when it comes to election time the opposition parties agree between each other that for any seat currently held by the ruling party, only one of the opposition parties will put forward a candidate against them. The aim of this is to reduce the effect of split votes and maximizing their chance of removing the incumbent representative. The opposition parties agree beforehand which of the parties will put forward a candidate for each of the seats (the parties will also have some data indicating the areas where they have the strongest support).
Are there any reported cases of this happening in the past and what was the public response in those cases? Did the public consider it to be undemocratic, corrupt or a legitimate political tactic?