- The adverb increasingly is one of the 117 mis-spellings listed as 'Common difficulties' in the section on 'Spelling' within 'Writing' in UEfAP.
Both the verb and the noun increase (and derivatives such as increased, increases, increasing and increasingly) have occasionally been spelled since Middle English with the initial vowel 'e-', as 'encrese', etc. This is now regarded as a clear mistake. Don't do it! - spell increase etc with an initial 'i-': increase.