The Met now have subsidised travel arrangements which they pay for, and have a card which must be produced with their warrant card. Unless it’s changed again recently. Regarding police officers ravelling free in general, my rule of thumb was that if I ever said a warrant card, whilst carrying out my duties I’d happily let them travel on it, regardless of what the technicalities of the rules say. The only proviso was that if it kicked off, I’d be expecting some assistance, and that if they were drunk as a skunk, they should really be buying a ticket. Not me being awkward, but for their own protection as much as anything, because they’d not be much use if it kicked off but may still try and help, getting themselves in to trouble in the meantime. Likewise if they’re out with their family and won’t be in a position to assist. Best to keep under the radar in these situations and surely only step in if it gets really out of hand, or make a sneaky phone call from afar? It’s not necessarily for my benefit, but for other staff who may be involved too, or members of the public who see the warrant card being shown. Even BTP aren’t entitled to free travel outside London officially. (May be different in other large cities like it is in London). I should point out that I was never a guard, not revenue protection, but part of my remit was dealing with ticketless travellers and report offenders etc.