I will be leaving AU on my AU passport and enter England in transit to Rome.

I assume I will need to clear immigration in London and intend to use my Italian passport.

Now I come back to London by rail and again will enter using my Italian Passport. I then leave for the US and assume that it will be best for me to use the same passport leaving London and entering US.

Will either be okay or is it best to use my AU as I will later be leaving for AU from LAX and returning to Brisbane where I will need to use my AU passport.