The Jamie Oliver Explorer BBQs work with a so called 'flamethrower' ignition. More information on this can be found on the FAQ page.
The following image shows the knob of the Explorer.
2. Full power
3. Low power
To ignite you have to keep the knob on 1. Push it and turn it to the left while holding it pushed. When the burners are ignited you can let go of the knob, and turn it to the hight you want.