Bluetooth HC-05 AT Commands
I got there in the end with this. Bear in mind the following conditions when trying to send AT commands to the HC-05:


The default baud rate on my module was 9600, not 38400 as described in certain places
If you make PIO11 (key) high (3.3v) while the module is on, it will enter AT command mode but will retain the default baud rate
If you power the module up with PIO11 high, it will enter AT command mode but the baud rate will be set to 38400
All AT commands must end with Carriage Return and Line Feed (\r\n)


The key bit for me was sending AT commands CR &amp; LF enabled on transmit.