Tree removal

We looked at a house that we were planning to buy but there are a ton of work to be done in the house before the house can be "lived in" legally.  One of those is the trees.  We were told by the vendor that the trees there (3) need to be removed   Apparently, the roots have gotten into the sewer pipings so we would have to remove them.  They are about 6-7 inches in radius.  The vendor kept saying they are an easy job but does anyone have any experience with this?  How much do these jobs usually cost?
Thanks in advance!

I would call your local authority (the local authority where the property is) to see if they have an anti crime measure for tradespeople:

http://www.direct.gov.uk/en/Dl1/Directories/Localcouncils/index.htm

such as http://casac.org.uk/

And I would contact someone from the Arboricultural Association to get a properly trained person to do the job:
http://www.trees.org.uk/index.php

You might also try a local college with an arboricultural course to see what they recommend or if they can do work at a reduced rate:

http://www.trees.org.uk/downloads/careerpack2010.pdf

HTH.

Oh thanks for the links!
I will definitely look at the options for a reduced rate