The couple, in a surprise move, have turned to the agency that also works with Nationwide Building Society, NHS Cancer Screening and mobile company 3.
Lewington, managing director of Hanover, said: "At the moment we're providing temporary press office facilities for the McCanns. Justine (McGuinness) has been overwhelmed by the press interest.
The case is very fast moving and our position could change by Monday or Tuesday, depending on what lawyers tell us over the weekend.
"The McCanns have been treated extremely badly by the press, it's only right to help them out."
The McCanns are fighting to clear their name as allegations and suspicion rises concerning the disappearance of their missing four-year-old daughter.
The McCanns previously used Bell Pottinger crisis management consultant Alex Woolfall (who represented holiday firm Mark Warner), Sheree Dodd, a former spokeswoman for the Government, and former treasury special advisor Justine McGuinness.