Ok - update. The next 2 days he played at nap time as usual until we eventually gave in and got him up - so no naps. We put him to bed early 6pm and both nights he went straight to sleep and slept 12 hrs. Today I Didn't even bother trying for a nap because I could see there was no way he was going down. He got tired in the afternoon about 4ish and half heartedly tried to nap on me but didn't. Hes been fine in the afternoons the past couple of days with no naps - even when he was in his pram at 3-4pm on fri when i really thought he would nod off, he didn't. I put him to bed early tonight and he was asleep at 6, no fuss.
The past 3 nights, including tonight, when he's gone to bed early, he's had brief early evening NWs (easily settled).
I'm thinking he is dropping the nap but is struggling a little and it's catching up with him, hence getting tired late pm today. The early eve NWs I'm guessing are due to OT. I'm thinking of trying putting him to bed about 17.30 tomorrow night if things go the same as they have been. He always wakes about 6.15am so I think I need to help him tag more sleep onto the beginning of the night as he never tags it on to the end.
What do you think? Does it sound like he's nap-dropping? Anybody know of any other LOs that have done it this early (nearly 21 months)?!