... ILR/Indefinite Leave to Remain - as the term implies - simply permits a foreigner to live here without a time limit ... albeit, of course, it's revocable in the event of he/she returning to *live abroad. (Unsure of for *how long!)
Citizenship, in contrast, is [generally] only revoked if the holder is convicted of a serious offence ... or becomes otherwise ineffective through [voluntary] renunciation.
's certainly my understanding of the situation.