They don't actually list the invidual ingredients under 'flavourings' - I believe they famously went to court to defend their right to not give away their secret recipe? - so I don't know how I'd go about figuring out what E number it might be...

I don't feel like I'm crashing afterwards, no... the staying awake bit lasts so much longer than the giggling bit that eventually all I want to do is get some sleep - if left undisturbed when I finally do get to sleep, I wake up feeling okay...

I suppose come-down is a relative term anyway - depends how far you're used to falling after a good night out...