Evidence was being gathered "against MPs, judges, media entertainers, police, actors, clergy and others," the IPCC said in a statement.
It said it was now looking at 17 allegations of a police covering up child sex offences between the 1970s to 2000s.
It is alleged that criminal proceedings were being prepared but a senior Metropolitan Police officer ordered the case to be dropped.
The allegations concern "suppressing evidence, hindering or halting investigations," the IPCC said.
Last week it was announced that 14 allegations relating to similar matters were already being investigated.