It looks like a picture winged fly. I see them around, don't think they cause any trouble.

Floral you have a good eye for plants not native to the British Isles! I saw a funny picture on the web years ago: at some botanical garden in the UK is a Toxicodendron sp. in a wrought iron cage. If you cut junk or invasive plants at the base, you ought to treat them to stay dead or else you will be back to cut them again, and again, and again. My preferred method is a commercial glyphosate diluted to 25% and mixed with a bit of surfactant and blue dye for marking purposes. Bring a 3/8" inch drill, dental irrigation syringe and herbicide solution to "job site". Drill hole in cut stems and fill with the dyed "roundup" solution - aiming for at least 1.5" deep. Guaranteed to work as long as there's no rain to wash it out in 24h. Dose roughly as follows: anything < 1 inch, 1 hole, 1-4 inches diameter, 1-1.5 holes per inch diameter around the edge, > 4 inches diameter, a hole every 2-3 inches along the outer edge. (hopefully you didn't let the weed tree get that big!)

Earwigs are supposed to be a neutral pest which feeds on dead garden materials. But to me when they are present in high numbers they're just the cockroaches of the garden. At my previous home they were all over the place and would invade my peach trees. Sometimes ripe peaches will develop a tiny opening at the stem end where these cruddy critters would find their way inside the peaches and make a home inside around the pit. I'm glad they are rarely found here at our new digs. I did not grow potatoes at my previous home so not sure if they'd be a troublemaker for spuds.

Yes, L. inflata will try to blend in but the foliage is a bit coarser than L. siphilitica and the flowers tiny as you confirmed.