I've just found some balls of chunky wool in my cupboard like you do
Thought I would knit my new baby nephew a jacket
does anybody know of a free pattern as I would like to get started

A good place to look for patterns is http://www.knittingpatterncentral.com/
You will need to look carefully at matching the tension.

Ive got a couple of babies chunky jumper patterns if you cant find a jacket.