The following chart is a proposed raw measure elaborated on https://www.nomisweb.co.uk data, retrieved from the London Data Store.
Impact of Italian first time workers on London job market by London borough of residence 2013-14
The measure is a raw one , and it doesn't have any other particular meaning than to show the impact those incoming Italians may have on the working population dynamics of a given borough.
To be absolutely clear, this doesn't show, actually cannot show, if Italians may be taking all new local jobs, or that they may be "stealing" jobs to people previously living on a particular borough, but it is more of measure of how much Italians tend or like to move in on a specific borough when they first enter the job market in London, in relation to that borough job market dynamics.
Italians may be pouring on Brent, but this may merely means that the decrease of the number of local active participants in the job market may be partially due local people finding better jobs and moving to other districts, as they are substituted by Italians (and perhaps other overseas workers) with lower job perspectives.
 it is basically a ratio of the number of NINo registered for the first time to people moving in UK from Italy to the number of job positions created by and for residents of a given borough in the given year, in case of job creation, or otherwise to the number of job position destroyed by and for residents of a given borough in the given year plus the number of NINo registered for the first time to people moving in UK from Italy, in case of job destruction, my Excel formula reads as:
This cannot show incoming Italians are taking all new jobs on a particular borough as the borough referred is the area of residence, not necessarily where they found their first job.
=IF('2005-2013'!AW4 [less than] 0,(1+ABS('2013 Overseas Pressure'!C5/'2005-2013'!AW4))*100,(100*'2013 Overseas Pressure'!C5)/'2005-2013'!AW4)