Got it! You push the white/clear bit of plastic
inwards, rather than outwards. The rest of them you push the colour coded bits on the sides and slide the fuel lines off. Have 5 pieces of tape handy to cover the lines you've pulled off. Then you "just" yank the filter straight up. I used a screw driver wedged in from the back of the filter through the holes in the back of the holder plate to move the filter upwards by twisting the screw driver. It then came off quite easily.
Push the new filter back on, then connect the fuel lines up. Start with the middle on the right hand side as it's the only way to access the side-clip-buttons easily. Finish with the "special" one; the one to the engine. Then twist the fuel cock to have the lines aligned. Turn the "igniton" on a few times and you'll hear the low pressure pump go. Twist the cock back. Start the engine. Done!