Hi - Just going through the process myself with my Montesa - to start bike has to have everything working ... no play in bearings, linkages, all suspension, straight wheels, non rusty tight spokes, proper silencer - no leaks etc etc - basically all the normal stuff to make it ride safe. Can be MOT'd on frame number - you do not need - lights of any description ( if you only want a day light MOT - much more envolved if you want a full MOT - not even a brake light ) or speedo - you need a horn - constant tone - not a sqeezy bulb type.
Once MOT'd you will need a letter from the importer ( or a main dealer ) confirming the age of the bike to register it at your local vehicle taxing centre with a form v55/5 - pay a one of reg fee