Focus fuel gauge problem

[coopenhagen]

Apologies if this has already been covered, I have used the search and not found anything.

I have a 2001 facelift 1.6 Focus LX and am having a problem with the fuel gauge. When the ignition is off, the needle moves to the midpoint, but then when the ignition is on moves to the correct point. Any ideas what could be causing this, and what can be done to fix it?

Cheers,

Dan