On a quiet Friday evening, an otter and a fox trot through Lincoln city centre. The pair scurry past charity shops and through deserted streets, the encounter lit by the security lamps of shuttered takeaways. Each animal inspects the nooks and crannies of the high street before disappearing into the night, ending the unlikely scene captured by CCTV last month.

Unlike the fox, the otter has been a rare visitor in towns and cities across the UK. But after decades of intense conservation work, that is changing. In the past year alone, the aquatic mammal has been spotted on a river-boat dock in London’s Canary Wharf, dragging an enormous fish along a riverbank in Stratford-upon-Avon, and plundering garden ponds near York. One otter was even filmed causing chaos in a Shetland family’s kitchen in March.

Janice Bradley, head of nature recovery for the Nottinghamshire Wildlife Trust, says: “Twenty years ago, they were almost nonexistent. Then we saw them coming up the River Trent from other areas. Now, we’ve got records of otters in virtually every river and watercourse in the county. It’s remarkable.”