Three teenage boys were convicted for raping two girls in Fordingbridge.
The attorney general suggested some other politicians' policies on small boats amounted to letting people "drown in the sea".
Lord Hermer tells the BBC he wanted "detail as quickly as possible" after hearing about the case in which the rapists were spared custody.
The prime minister said it was "right" that the sentences were being urgently reviewed.
Derek Johnson, from Gloucestershire, admitted 16 offences relating to girls aged between 13 and 16.
It follows the collapse of a trial, involving serious sexual allegations, in its fifth week.
The Attorney General's Office will consider whether Reece Galbraith's jail term is too lenient.
The Meriden and Solihull East MP says he has written to the Attorney General over Daniel Clarke's jail term.
Prosper is currently serving a minimum of 49 years in prison for murdering three family members.
