Peugeot 407 1.6 Saloon Alloy fitment?

You have to fit the wider tyres to the rear axle for safety. The problem is you have obviously bought second hand - so you take a chance as to whether the wheels and tyres are suitable for your car. I have no idea whether you need spacers or anything else - because you have not told us the PCD and offset of the wheels you have bought. If you can get them to fit they should be legal.