David Parker wrote:

I have some white mould growing on the base of my grass all
over the lawn. The grass is ok after about an inch but very
brown low down

Could be powdery mildew:

http://www.ipm.ucdavis.edu/TOOLS/TUR...dispowder.html

or a slime mold:

http://www.ubcbotanicalgarden.org/po...m_cinereum.php

What have your weather conditions been for the past month or two? Cold,
damp, cloudy, not much wind?

Does your grass in the affected area get much sun? Air circulation?
Drainage?