Concert Party
This is not the kind of party you want to find yourself involved in -in the London stockmarket, it's illegal!
A concert party describes an arrangement between two or more investing parties who act together (in concert) to manipulate the price of a share or commodity.
In the London stockmarket, the UK Panel on Takeovers and Mergers (POTAM) frowns severely on such a situation where individuals have agreed in private to co-operate to take control of a company by purchasing the shares in the market without announcing the fact that they are acting together.
The code on takeovers requires the bidding company's offer document to spell out in detail all relevant shareholdings owned by the offeror and also by anyone else acting in concert with them.