There are earlier articles saying some work has been going on, I think the scale increase is recent though.
I assume the slow UK response will be down to the UK water authorities being private and wouldn't do it off their own back while public health has been rundown to not have capacity for it.
https://www.bbc.co.uk/news/health-54646451
Covid: Sewage sites to test for more traces of virus
Published 23 October