Ford Cargo Parking Light?

I have a Ford cargo 0813 and recently took it out for a decent drive after the winter snows etc.
Having driven for some 40 miles or so, I noticed the Parking (Brake) light came on on the dash. I have taken it out again since then and after a few miles 10 - 20 the same thing occurs. Can anyone assist?

Lurky
February 2010