The CAA used to publish the numbers of diverted flights at UK airports but I cannot find them from a quick search. However, perhaps the numbers of cancelled flights at UK airports would have some relevance to diverted flights, as the former is often the result of the latter. On that basis SOU seems to have had more cancelled flight in 2019 than virtually any other UK airport. Of 32,529 SOU movements around 3% were cancelled while at LCY around 2% were cancelled - both having CAT I ILS.
Maybe someone has access to the actual CAA diverted flights statistics.