thanks to all for the advice - I listened to some soundclips as suggested and read some reviews on Harmony Central too.

My plan is to go for the Ibanez PH7 because it's cheapest (<£60)and I don't know how much I'd use the more esoteric sounds on the Boss PH3 / Ibanez PM7 / Digitech Hyperphase.

However, I'm also going to get a feedback/tb loop as per grover's suggestion so that I can make siren noises