About SETSThe decision to switch to an order-driven trading system was taken in 1997 and SETS (Stock Exchange Electronic Trading Services) has changed the way FTSE 100 and many FTSE 250 stocks are traded in London. AIM stocks also sometimes show order book on a mixed SEAQ/SETS screen called SEATS.
Instead of agreeing to trade at a price set by a Market Maker, prospective buyers and sellers can advertise through their broker the price at which they would like to deal, and then wait for the market to move in their favour or execute immediately at the best price currently available.
The order book automates the process of dealing in equities - first by matching orders to buy and sell shares, and then by executing them to create trades. Though being able to see the order book is available to ADVFN users, only LSE members can actually enter the orders direct.
The trading day for SETS securities runs from 8.00 hours to 16.30 hours on each Stock Exchange business day, subject to a random opening and closing adjustment. The opening of the market is preceded by an opening auction during which time brokers can enter certain types of orders for execution during an uncrossing, which starts the trading day. The trading day ends with a similar auction pre 16.30 hours.
Auctions may also take place during the trading day, triggered by substantial price movements in a security