There is no objection to spelling onto as a single word when it means ‘to a position on’: The book fell onto the floor. However, onto should not be used when the word on is an adverb attached to the preceding verb, as in Some people have reservations about using onto after a verb that is often followed by the preposition on. In a sentence such as We walked on to the end of the lane (‘until we reached’), onto would be incorrect. Compare We walked onto the end of the red carpet (‘we walked forward and stood on’), in which onto is correct. Sentences such as She latched on to the idea at once and I want to move on to another topic are, however, a grey area. Onto is increasingly being used in them, but the safer option is to use on to. The form onto has been used throughout this dictionary