Stick insect approx 5-6 inches long. It was 'dancing' on the sunflower leaves, swaying from side to side.
No interactions present.
Just come across your image via an internet search. I collate all the records of the naturalised UK Stick-insects, and can confirm that your specimen is a largish nymph of the Unarmed Stick-insect Acanthoxyla inermis. This species originates from New Zealand, as does the very similar Smooth Stick-insect. This latter species is only found in the Isles of Scilly on Tresco and St Marys.
The Unarmed Stick-insect is widespread in Penryn, having originated from accidentally discarded eggs in 1983. I can provide more detailed information on our naturalised stick-insects if you would like to use the online reporting system of the Phasmid Study Group with details of your sighting via this link -
Lat/Lng: 50.1, -5.2
OS grid ref: SW7733