Recently, ITV released a new 'Where Drama Lives' trailer for their autumn 2013 dramas. You can watch it here (if you're not in the UK, this might help you). Below are some screencaps of the three glimpses we get from the new Poirot episodes:
Now, this I can say with a 100 % certainty is from The Big Four. That should be obvious for anyone who's read the novel. The setting looks a bit different from how I remember in the novel, though, so I think we're in for some changes.
This is a lot more different to place. But based on the first and the next screencap, I'm tempted to go for The Big Four here as well.
Again, I think I can safely suggest that this is from The Big Four, very possibly the climactic scene (which, if the rumours are correct, has been changed quite substantially). The bow tie and the suit are the same as I've seen in a few location photos leaked from that scene. Based on this trailer for autumn drama I think we can now assume that November 2013 is the most likely air date, as has been suggested online. Lots to look forward to!
UPDATE: Guess who made a brief appearance in a second ITV trailer today (9/9/13)! See ITV's press release for the trailer and the reason behind it:
Obviously, this isn't recent footage. David Suchet was added through post production techniques. They seem to have used footage from Series One (I can't identify which episode off hand) and then added it to the stuff that was shot specially for the trailer. Still, it's a cool way of marking the 25 years.
All photos copyright ITV.