At the end of june i travelled from edinburgh back to cornwall, i vaped all the way, no one complained, mind saying that i looked really grumpy as i had just buried my mum and was going back to confront the now ex about her daliances whilst i was away, i was a full on smoker at the time and was using an e-lite, albeit discretely.
hide it up your sleeve take a really deep vape exhale towards you nether regions and cock your leg, if anyone looks at you funny advise them to avoided the buffet cart!
This is how I do it.
Inhale a mouth full, then inhale it into your lungs gently. THEN, breathe in again... And hold it for a while before you breathe it out.
There were a couple of vids posted about stealth vaping. I can't remember who posted them now but the best one (and I tried both) was to take a lung full, then breath in again to help to vapour dissipate in your lungs then hold your breath for about 10 seconds. No vapour left I don't think I held for the full count of ten mind. But it worked. The other was to hold e-cig inside your sleeve, take a crafty vape and exhale down inside your top. This helped to lessen the cloud of vapour but not totally.
I've vaped on trains. Not been on a Virgin train lately, but I would probably stealth it unless I was explicitly told it was fine. Best way for me is, as everyone else said, to breathe in deep and hold it a good 10+ seconds. When you exhale, virtually no vapour will come out. The way I see it - if vapour is the problem for any companies that don't want you vaping on a train, then if there's no vapour it's no different to a nicotine spray or inhaler.