Sooooo on the tube in London....?

Yah it's illegal, you could probably do it with a travel card though (not saying you should lol and you might get caught), just that once I have an off-peak travel card because it was cheaper but I didn't know about the off-peak/peak stuff, and I used it in a busy station in peak hrs and it didn't work so I asked my friend in front of me, who ped the barriers, to give me theirs and the security/ticket guy sat there watching me lol but did nothing, (if you get caught you'll get a fine or told to go and pay for the correct ticket, as what happened to the other people I was with later on in our journey when the police came lol, I had the money and good intentions but just the wrong ticket, not sure about the others, we ended up buying the extra ticket and no one was arrested or anything lol.)