You probably need to give a little more information County is a trim level
which can apply to Disco Defender ( ok I know strictly speaking a 90/110
county is not a defender ) or Rangie- type and year would help -Nige has
some experience of these problems and others have also suffered at the hands
of mobile phone masts which may do all sorts of nasties to the
alarm/immobiliser circuit have a look at
http://groups.google.co.uk/groups?q=range+rover+immobiliser+bypass&hl=en&lr=&sa=
X&oi=groups&ct=title
 for some of the fun and games.

Derek

I once had an intermittent on my 110 County (300Tdi) and I did a get
home fix which involved running a wire from the cigarette lighter
socket to the terminal on the fuel pump.

Later, I wired this in via a hidden switch under the dashboard which
avoided all problems.

David