Mot is a 45min yearly check to see everything is road worthy on a vehicle, every vehicle over 3 years old has to get one.
Plg ( private light goods) is the category of the vehicle, this category is for cars, which quads are classed as in the uk. No motorcycle license required.
Let us know how that works out, agg vehicles are supposed to be fitted with a seatbelt and roll cage by new laws coming into place. You'll also need stock pipes as toomeys don't have Yamaha stamp.
http://www.quadtech.co.uk/
Where are you based?