In and out with Oyster (main line station)

IIRC you'll be charged a pound or two.

You might be able to buy a platform ticket from the booking office, though when I tried this at Lime St the booking clerk's brain started to melt.

The barriers are often left open in the main station (platforms 0 to 8) anyway. You are unlikely to be challenged if you are seen walking off a platform from which a train has just departed.

In and out will be either a minimum (£2.40) or maximum (£5.60 or £7.20 peak) charge, depending on how long elapsed between touches.

If the barriers are in operation just ask a member of staff. They're friendly enough and will let you through if you're clearly accompanying someone. You'll find the staff downstairs less than accommodating to refund that maximum charge! (We are technically able to, but prohibited as it's not because of our services.)

Not universally.

Also, since the ticket machines were upgraded a year or so ago it's a very difficult and convoluted process to get platform tickets from LUL POMs... I only found out myself last week after a year of asking. 🙄

such variations - all the main line machines at Stratford sell tickets from other stations so you can extend your Travelcard or Oyster if you touch out at places like Shenfield.

Apparently you choose "Select Destination" and then either type in "pla" as a destination or you select the station name you are at [1]. That should bring up the option of purchasing a platform ticket. I haven't tried it myself and only found out courtesy of a "document" I was sent. I confess to being slightly amazed that Platform tickets have survived all the ticket and process rationalisation that has accompanied "Fit for the Future".


[1] e.g. Upney if you are at Upney station, Bow Road if at Bow Road etc etc.