No evidence against them at all, what can they do?
I would take a close look at what kind of game those informants are up to. Maybe they are trying to mislead rather than help the police.
either that or MI5 is sending a "message"
That was my thought. The whole thing was a 'game' on the police, etc. Afterall, they said that they'd seen the cops/etc watching them for weeks, they knew they were under survellance(sp).