I don't believe that Italy are testing everyone with symptoms.
From what we are being told, most cases in the UK still have links with known cases or are people returning from abroad. We are not seeing widespread community transmission yet in the UK- and I do believe we are testing enough to spot this.
Of course Italy are testing more people than us- they are in a completely different scenario to us.
We would know if there was a huge spike in people with viral pneumonia being admitted to hospital, as well- things like that hit the news.
I feel like some people on this thread are determined to convince themselves that things are worse than they are!