Any lot held in single and separate ownership on the effective date of this chapter or after the enactment of subsequent amendments thereto which does not meet the minimum size or width requirements of the zoning district in which it is located may be used for any use permitted in that district, provided that all yard, height, coverage and open space requirements of the district are met; provided, however, that if two or more lots, combination of lots, or portions of lots with continuous frontage in single ownership are of record at the time of passage or amendment of this chapter, and if all or part of the lots do not meet the requirements established for lot width and/or area, the land involved shall be considered to be an undivided parcel for the purpose of this chapter, and no portion of said parcel shall be used or sold in a manner which diminishes compliance with lot width and/or area requirements established by this chapter, nor shall any division of any parcel be made which creates a lot width or area below the requirements stated in this chapter.