Disclaimer: I dont live in the UK , i'm not very familiar with travel market there. This is how I book my tickets
-Check out you flight options on
http://www.flightlookup.com/- google for uk online travel sites like expedia.co.uk , get a general idea on pricing
- Go to your local travel agent and ask them to beat the online quote. Try push them as low as you can , the agents have generous margins
- You normally can't get good prices buying directly from airlines, they will not undercut agents