London bus with 16 CCTV cameras inside

It's Bank Holiday Monday here in the UK, so this morning we took the kid to the zoo in Regent's Park on the 205 bus. The bus we got was quite a new one, and right by the driver was a screen showing the feed from the sixteen CCTV cameras on this one bus. How much of that footage to they actually archive? For how long? And how much of it do they lose track of?

SIXTEEN cameras on the new London bus, 205, Islington, London, UK.JPG