Enrol is the standard spelling in British English, which breaks the general rule that British words carry with them an extra consonant. In many cases, such as traveling-travelling, canceled-cancelled, totaled-totalled, labeled-labelled, etc., it is the British spelling that contains the two –ll’s.
But, in the case of enrolment, the standard spelling in British English only has one l – enrol and yet in past tense it is – enrolled.
in American English the word has two ll’s – enroll and enrolled.
The origin of the word
The word enroll originated from late Middle English (formerly also as inroll ): from Old French enroller, from en- ‘in’ + rolle ‘a roll’ (names being originally written on a roll of parchment).