Yes, the second time I plugged the 5V power source into the power jack on the arduino, when I did this, the arduino was powered and the LEDs lit up.
The first time I plugged the 5V power source into a dc jack to terminal block with the ground and power wires from the LEDs wired into this accordingly (with data, power and ground also from leds into the arduino digital pin 6, 5v pin and ground respectively) - this initially worked, then stopped working - so something here is not working as normal - could the jack/terminal block have broken (does that even happen)?