Please offer me a seat!

Not all disabilities, treatments or illnesses are visible, so London Transport are trialing a Please offer me a seat badge. If you qualify, or you know someone who does, please pass it on. I'm guessing they'll want someone who uses Public Transport in London reasonably frequently and who is willing to give feedback on their experience of using the badge back to TFL.

It sounds like a great idea, and I'm wondering if it encompasses (for example) people currently in chemotherapy and the like. Dad had the odd difficulty of getting told off for sitting or leaning on things (such as when visiting shops or Stately Homes) and it was awkward having to explain to people, "yes but... he really needs a breather."