Fast Market
This is a technical term used by the London stockmarket to describe a situation in which share prices are changing more rapidly than the prices actually quoted on the SEAQ service by the market-makers . Such a situation means, of course, that a market-maker's price may well be out of date when you try to deal on it.
Therefore, when the Exchange authorities declare a fast market, the market-makers are no longer specifically obliged to deal at their quoted price but may vary from it. That is to say, the price on the screen becomes indicative, not a firm price.