I've had this issue on a couple of times and wonder if others have had it / have any thoughts. It concerns occasions when an XC train is made up of 2 units, and I've experienced it on both a Voyager and a Turbostar (the latter last weekend). For fairly obv reasons the guard with ticket issuing facilities is in one half and the only staff member in the other half of the train (the part with the driver) is the trolley host, unknown to me on boarding which half. I get on the train and go to 1st to sit down, (it's empty - on both occasions) and the trolley host says I can't use it without a 1st class ticket to which i ask for an upgrade. Trolley host explains they can't sell the upgrade, only the guard can, and they can't walk through so I can't use it. Having had the situation before I recall thinking how daft this is and insist on sitting in the empty compartment. Trolley host is of course unhappy but when I say 'if there is no gaurd who is checking the tickets?' to which the answer is no one. I explain that I will very happily go to find the gaurd when I get off to pay, since they can't come to charge me. I was polite but firm, the host was very unhappy but left me to it, saying she would report the matter to the guard. It's really bonkers. If the trolley hosts could sell me £10 etc of drinks from the trolley why can they no sell a £10 etc upgrade? What other business would actually turn down offers of payment from customers and leave products (empty seats) unsold, on an otherwise busy train? I had promised the host that I wanted to pay so I did indeed go immediately to the gaurd on the platform in the dwell time with my money ready. I had indeed been reported to the gaurd who knew of the situation. The gaurd explained that she did not have time to do the ticket, thanked me for my honesty in offering to pay, and basically used her discretion not to charge me. I didn't feel good about that as I had promised the trolley host I WOULD pay, so I popped in to the ticket office (who were quite bemused by my request), but as the XC w/end upgrades are on the system, were happy to take my money and issue me with a ticket. But I do think XC's policy of not allowing people to pay upgrades to custmer host staff that have money handling facilities is really pretty daft - esp as a good few of their trains are made up of double sets.