Just to let people know, I got stop by an unmarked car Yesterday (Ludgershall/Tidworth, Wiltshire) and was fined £30 fixed pently for my Tints. This was for my front side windows on my Mk5 Fiesta ZS, the device they used said my Front window had the Ford standard 85% tint and my side tints came up 35% on the device.
My brother inlaw John has dan's@fastfords Zetec-S Mondeo and they are lot darker than mine but Dan quoted them in the mag being 70%, I've advise John he best remove them but that upto to him.
Mine were on the car were on the car when I brought it about 4 years ago, and I was advised they were legal.
So my advise is Don't bother with tinting the front side windows, unless you like give the Police £30 every time they stop you.