I have a 2

I have a 2.2dci diesel X-Trail. The car had 3/4 tank with diesel but put £20 of unleaded by mistake I run the car for 20 miles home it was not running well, I called a company to drain the whole tank, I later filled the tank full with diesel, but now have a warning light emissions permanently on. It runs well for a 1mile or so, but sluggish, but by switching engine off and restarting it runs okay but the emission light stays on permanently.