Clickettman - as i said further up the post, you can buy hubcentric spacers in 16mm which would bring the Focus RS wheels near on close to the escorts offset of 25mm.

42mm offset with a 16mm spacer = an et26 (1mm out)

if you wanted them to sit as the et15 that many suppliers chose to sell 18" wheels for the escort cossies (such as Martoon on the Comp MO's, and Paul with the Monte/Ripley wheel)
then you would need a spacer of 27mm!!