At the end of a sentence we place a full stop (or other punctuation). Do we NEED a space after the stop to begin the new sentence? I have been told it is correct grammar to not use a space after the full stop.
The space after the full stop is mandatory.
There is, however, a divergence as to whether one or two spaces should be used in this context. There doesn't seem to be any consensus on this issue, and it is more a matter of formatting than (strictly) punctuation.
For a much fuller answer to this question, see How many spaces should come after a period/full stop?