I am very wary of contradicting the statements above regarding the seats in RAF T4 trainers, as I am neither a pilot nor an aeronautical engineer, but I have a very specific memory of a flight in a T4 in 1957 which did NOT have ejection seats. There is an archived thread in this forum dated about Oct/Nov 2011 and titled Canberra Bomber, which covers this very subject in quite a few posts, (several of them by me), and quite a lively and informative discussion took place about the seating details. A very clear drawing posted by longeron illustrated the general arrangement of seats in a T4 without bang seats.
The conclusion seemed to be that some early T4s were in service without the Martin Baker bang seats that were fitted to later examples, and that the aircraft I flew in was probably one of those.