How much should plumbers cost in SW London?

Chubacheroo

As you can see from the thread I just posted about our dodgy shower, we've got plumbing problems. We've also go a leaky boiler thing and sink which seems to be backing up. So it's a bit of a plumbing disaster. With a baby due next month, I really want to get someone around to just sort it all out once and for all.

We've got plumbing insurance, but this obviously only covers emergencies - which we have had to use, but obviously, they don't fix the root cause.

So what I was keen to find out was:

1. What would be a reasonable amount to expect to pay for a plumber in SW London? I realise that this depends on what they have to do...
2. Does anyone know of a good plumber in the area who they can recommend?
3. Do they guarantee their work?

Thanks muchly in advance!