LONDON — A British judge sentenced a notorious serial rapist to at least 27 years in prison Friday for a spate of attacks on elderly people that lasted almost two decades.

Delroy Grant — dubbed the “Night Stalker” — was convicted of attacks on 18 elderly men and women between 1992 and 2009 following a lengthy investigation. Police say the number of Grant’s victims is thought to be substantially more than that.

Judge Peter Rook said he considered giving Grant a life sentence — meaning he could never be released — and noted the crimes were so serious they were not covered by normal sentencing guidelines.

“Your offending is in a league of its own,” he said at Woolwich Crown Court after hearing statements from Grant’s victims and their families.

The attacker broke into homes, cut phone lines and crept into the bedrooms of his elderly victims during ordeals that lasted for hours. The victims were mostly elderly women; many were blind, deaf or had diseases such as Alzheimer’s or Parkinson’s. Some said the masked man woke them up by shining a flashlight in their faces.