As I have noted before, this attribution work is really difficult, and takes a lot of computer crunching, but I don't see much reason to doubt its conclusions.
The other caution in the article is this:
Dr Schaller notes that the results must be understood in context, and are specific to the UK in winter. "It all depends on the region and season considered. Climate change might increase, decrease or have no effect at all on flood events," she told the BBC.
"Hirabayashi and co-workers, for example, showed that floods are expected to decrease with climate change in Central Europe. So our results are only valid for the southern UK and for winter months."