Mahran as a named company remains subject to sanctions and embargo by the US State Department separately from the CIAD 2010 act.
They are considered a wing of the Iranian Military and in support of terrorism by US State agencies.
Specifically they have been implicated in directly providing airlift the the Republican Guard into both Syria and Northern Iraq and for transporting large arms cashes from/through Iran from Russia China and the DPRK to the Asad Regime in Damascus.
Suffice to say they can't legally get their hands on shiny new Airbus or Boeing aircraft for the foreseeable future.
They are certainly operating flights for Syrian Air at the moment using an A300 within the region.
As for restarting flights to the UK -the US are leaning on UK agencies at the moment to deny authority.
BTW they never started Gatwick but have flown to both Manchester and Birmingham in the past.