For England and Wales, the area of glazing is more likely to be determined by the need to provide purge ventilation which can be 1/10th of a room's floor area if the windows open to only 20 degrees, as described in
Approved Document F, Appendix B.
Approved document L1A 2010 states, in clause 4.27, that no minimum daylight requirement is specified. However, as a general guide, if the area of glazing in a dwelling is much less than 1/20th of the total floor area, some areas of the dwelling may experience poor levels of natural light resulting in the increased use of electric lighting. You should note, however, there is a warning that too much glazing can lead to solar overheating and so there is a balance to be met between the provision of natural lighting and solar heat gain.
The Scottish Technical Handbook for domestic buildings does, however, describe a recommendation to provide a minimum of natural light in section 3.16. Every habitable room should have glazing, that will let in daylight, which has an area equivalent to 1/15th of the room's floor area or 1/15th of the combined floor area of an extension to an existing room.
SAP 2009, which is applicable to both Scotland and, England and Wales, considers, in Appendix L, the contribution from natural lighting when calculating the energy requirements of electrical lighting. A reduction factor is determined using the total area of glazing, the amount of light that passes through the glazing (light transmittance factor) and any shading provided by neighbouring buildings, trees etc (light access factor).
The Code for Sustainable Homes awards points for daylighting under category 7, Health and Well-being, where the aim is, "to promote good daylighting and thereby improve quality of life and reduce the need for energy to light the home". There are three points available, one awarded for an average daylight factor of at least 2% for kitchens, one for an average daylight factor of at least 1.5% in living rooms, dining rooms and studies and the final point is awarded if at least 80% of the working plane in these rooms receives natural light. The daylight factor is a comparison of the natural light levels within a room and the natural light levels in an unshaded location outside and the working plane is a nominal surface positioned 0.85m above the floor. Further information on natural lighting can be found in BS 8206-2:2008 Lighting for Buildings – Part 2: Code of practice for daylighting.