Yes, putting the Key into the lock in the boot, you turn it to the RIGHT (clockwise) to manually lock it.
Turning the key to the left should unlock it. You might have to try turning the key anti-clockwise as far as it will revolve?
I also find I have to use the keyfob TWICE (for central locking), as the Boot unlocks on the 2nd press - while the doors unlock on 1 press....