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immediately is one of the 117 mis-spellings listed as 'Common difficulties' in the section on 'Spelling' within 'Writing' in UEfAP.

The adjective immediate and its derived adverb immediately have two '-m-'s each, as well as an '-e-' at the end of the fourth syllable. There is no '-e-' between the '-l-' and the '-y' of the adverbial suffix -ly (there never is).