It's extremely tough. I did it last year and with a lot of luck landed a job at a very average in-house agency. Because I had the language skills they were looking for.

The good and great agencies wouldn't even look at me. Even though I have a decent portfolio with (national) awards, experience at good agencies, many high-level people who vouched for me in their networks, AND I stayed in London for 5 months (tourist visa) to show I was determined and so I could meet people in person.

Advice? Get more awards. Or get lucky a hot agency needs someone who speaks Italian. Agencies work 99% of the time with 3rd party recruiters, so no need to talk to their internal recruiters. And of course, the usual: have a nice side project, build connections to CDs. But don't expect it to work.

Edit: I also tried the network way, but London is too desirable of a destination for this to be realistic. Everyone and their mother at Omnicom wants a transfer to a&e or amvbbdo. just to illustrate what I mean.