^^^ what davidjohnson6 said.
Until last year I used FR regularly on a relatively thin domestic route; i.e. one that was always included in the promotion on FR's homepage. While it lasted, I hoovered up as many £0.01 and £1 fares as I thought I might night and used maybe 10 - 15% of them. However from 2009/10 onwards, then £0.01, £1, £3 etc sales started to dry up. While there are still some single digit sales from time to time, it seems revenue management are pushing even the cheapest promotional fares up.