If they've extended the run for Grease in the UK, then I would guess that ticket sales are also doing well there.  It doesn't look like the show has a web site as the Broadway production does.  The only thing I've found so far is the "Grease Is the Word" board on ITV.  I didn't think that Danny B. and Susan McFadden were as strong as Max and Laura, but they should be fine in the roles.  Different director and more of the original approach, I think.