This is more common than you would think. If the forms aren't sent recorded they seem to get 'lost', I know mine did and I know of a few others too, plus yours, hmmmm a pattern occuring ?
You's have got me worried now men, was going to send it recorded but just sent 1st class, i probably could of even handed it in personally as i work about 5/6 mile away from the ponteland HQ where i sent my forms to. i'll start panicking if i havent heard anything in a couple of weeks.
Don't wait that long, give it a couple of days and phone to check everything arrived ok. Just puts your mind at