PlusMarkets, the small UK exchange formerly known as Ofex, has confirmed it has signed a reverse takeover agreement with a third party widely believed to be equity trading platform Turquoise, in a move that steps up the seriousness of a threat to the London Stock Exchange's stranglehold on UK share trading.

Plus Markets issued a statement today responding to a rise in its share price, saying: "Plus Markets Group plc confirms that it has signed a non-binding heads of terms agreement with a third party."