Smoking at revs

Just had mot done failed on emmisions as it starts to smoke after a few secs at revs. Does this point to valve stem seals? Is there any easy test to check without the exspense of of removing the head?

Got sore eyes from looking through forums, another possibility is the pcv valve? any views on either?

Ok no answers yet so here's an update :- removed inlet manifold (old type so will need upgrading to 2002> model as flaps are a little loose) flaps covered in oil and can see oil inside the head sitting there. So pcv valve or seals on valves?

Will give further updates but would like some opinions guys/girls

Update:- replaced inlet manifold, oil seperator and pipes. Removed o2 sensor and lamda sensor they looked a little sooted nothing else so looks like they are ok. Spark plugs lokk a little oily gave a clean put all back and still smoking!

There is no smoke on start up or while auto choke is warming engine, it doesn't start to smoke till it's warmed up - so any ideas? oil residue in exhaust burning off when hot? yet no oil on sensors! Would expect smoke on initial start up if it were stem seals gone as it has been sat for a couple of weeks yet its clear till it's hotted up??