From Traderpedia

Abbreviation for the Stock Exchange Automated Quotation.

SEAQ was introduced in preparation for the Big Bang and has allowed all transactions on the exchange to be carried out by telephone rather than as formerly on the trading floor.

[edit] How Does It Work?

The Stock Exchange Automated Quotation (SEAQ) service is the official trading service for the majority of small to mid-cap, domestic securities. On SEAQ all buys and sells go through a market-maker who acts as an intermediary. SEAQ is used for those stocks which are too small to be traded on SETS.

SEAQ provides real-time access to the quotations of individual market makers registered in every London Stock Exchange SEAQ stock as well as the offering or bidding sizes that they will trade up to. This level of access gives the name of the market makers looking to trade the stock, and allows traders to see which ones are showing the most interest in a stock and identify the patterns for each one.