Hi Martyn,
1) A Ni-Cad cell charges at nearly 1.4V, not only 1.25V which is its discharging voltage. Read about them at
www.energizer.com and click on their Technical Info. They still post info about their obsolete Ni-Cads. Look at their new very high capacity Ni-MH rechargable cells too.
2) You are planning to "quick-charge" the cells but don't have a method to detect and shut-off when fully charged. The Energizer site describes the nice
explosion that you'll have when all the charging power is converted to heat when the cell becomes over-charged!
3) Your diode is backwards and should be at the output.
4) Don't you understand? You don't need to "bring the voltage down". I agree with Nigel, you don't need a voltage regulator since a Ni-Cad or Ni-MH cell limits the voltage anyway. They are charged with current. You could charge them from a few million volts if you limit the current to their rating.
4) Your supply voltage is way too low for a single LM317 current regulator. It must be at least 3V higher than its output voltage to regulate properly as shown on its datasheet.
5) How can you have 4.1 ohms with two 8.2 resistors in series? Put the resistors
in parallel and measure the result to make sure.
I don't think the resistor values are correct anyway.
Your schematic shows mW which is power, instead of mA which is current.
6) I agree with Nigel, the transistors make lousy switches, use Mosfets.