One of the tasks when I'm volunteering on the DWT Brownsea reserve is manning the DWT gazebo at the end of the boardwalk. This is a public engagement role & we often have interesting conversations with the visitors. Today, we had a less communicative, but exciting visitor, which my colleague spotted on the desk. It was this gorgeous & small green-coloured Weevil. Vanessa ran it through Google Lens which identified it as Nettle Weevil (Phyllobius pomaceus). A search online that evening identified there are a number Phyllobius species in the UK, but Nettle Weevil looked the best candidate. I put the photo on twitter & bluesky.social and tagging it people who might be able to help, but I didn't get a lot of response.
However, a couple of days later, Jonny, one of the DWT wardens suggested it could be Polydrusus formosus. That looked a better fit on the face of it, however, I was struggling to find out much to conclusively identify it. Jonny retweeted my twitter photo and tagging it a few more people who might be able to help. I left it a few days, but as I didn't see any responses, I tried iSpot. A couple of days later I saw a response from Sarah Loving who came up with some really useful links & these words.
I am sure you're right that it's either Phyllobius or Polydrusus, but telling the difference can be tricky. There's a really good page here: https://www.eakringbirds.com/eakringbirds6/insectsphyllobiusweevils.htm
The difference they highlight is where the antennae attach to the head: on the top in Phyllobius and at the side in Polydrusus. It looks as if the antennae insert at the side of the head in your photo, but it's not totally clear. I believe that identifying these to a species often requires a specimen and examination of very small features. See the page here (very long and also quite technical!): https://www.ukbeetles.co.uk/green-weevils
To my eyes, the antennae come of the side of the head which puts it in the Polydrusus group of twelve species. Having looked at the UK Beetles link, then the only species that fits in Polydrusus formosus. Finally, I wanted to check its range. I searched on the National Biodiversity Network (NBN) website for this species. Not only is the species found in the Isle of Purbeck, but there is a record for Brownsea Island with the pin looking very close to where the gazebo is positioned. The final website I looked at is the Nature Spot website for this species which also supports this identification. It describes the habitat as "found on various broad-leaved trees and bushes in Apr to Aug".
Everything seems to fit for Polydrusus formosus. All the sites talk about the importance of having good photos and retaining the specimen to study under a microscope. To be honest, I think the good photo seems to be sufficient for the identification & I would rather live with the risk of the record not being accepted, but with the Weevil being able to continue to enjoy its life on Brownsea, than to see it killed for a 100% identification. It has taken several hours & fair bit of searching online, but I feel happy with the identification. Thanks to Jonny from Brownsea & Sarah Loving for their input.