I reproduce this email from Andrew Johnson at Tesco with his permission:
After our conversation earlier today I have made contact with [the landscaping firm] with reference to Whitchurch. They have returned the mail below suggesting that they have not undertaken works on the river bank at that location. However, they do confirm that they have carried out works as far as the top of the bank as per their usual annual maintenance programme last month.
Regardless of the above I have made it clear to [the landscaping firm's] senior management that their staff are to be aware of the issue & subsequently [the landscaping firm] have confirmed that they will not carry out any works on the river bank at Whitchurch (They have cascaded the information to their service engineers).
Furthermore we understand that the Store Manager has made an arrangement with your Whitchurch Water Vole Group, whereby he will request your help to clear any future vegetation issues we encounter - thus protecting the habitat/bank ecosystem and ensuring your Group are consulted prior to works.
I trust this helps to clarify any further concerns you may have, and we apologise sincerely whether [the landscaping firm] or others were responsible for the trimming works.
This is excellent news, especially as I could see from the header the email had been copied to lots of people. Well done Mr Johnson! Still not wholly clear who's done this strimming, unfortunately, but at least that's another group of people who work on the brook who now understand the importance of maintaining this precious habitat.