OP is flying to Italy. Italy is not in UK.
According to these sites it is still required for Italy:
https://infocovid.viaggiaresicuri.it/returningtoitaly.html
https://www.euplf.eu/web/index-2.html
and I just checked my Travel Ready on United and it is still required for Italy
You should be able to find it on your airlines website in the "travel ready" or similar section.
Or download it from here:
https://app.euplf.eu/#/
You only need to include the flight that LEAVES USA and the flight that takes you to Italy, along with the FIRST place you are staying. Each traveling adult needs to fill one out.
The purpose of this form is to notify you if you have been exposed anywhere along your way.
Important information
Passengers entering Italy are currently needed to complete a Passenger Locator Form via the EUdPLF application (https://app.euplf.eu/).
ITALY Information for travelers with Italy as destination country: All
passengers wishing to enter Italy, via all means of transportation,
will be required to complete the digital PLF (https://app.euplf.eu),
prior to entering the country. Domestic flights do not need dPLF
Passengers in transit who remain within the Transit Area of the
airport do NOT require to complete the dPLF. If for any reason one
exits the airport, a dPLF will need to be completed. One form must be
completed for each adult passenger; accompanied minors can be
registered on the form of the accompanying adult in the Declaration
section. In the case of unaccompanied minors, the dPLF must be
completed by the parent or legal guardian before departure. Check the
Italian Ministry of Health for further information:
https://www.salute.gov.it/portale/nuovocoronavirus/dettaglioContenutiNuovoCoronavirus.jsp?lingua=english&id=5412&area=nuovoCoronavirus&menu=vuoto
https://www.salute.gov.it/portale/nuovocoronavirus/dettaglioContenutiNuovoCoronavirus.jsp?lingua=english&id=5412&area=nuovoCoronavirus&menu=vuoto&tab=2