I have been looking up environmental factors influencing nectar secretions in plants,
High humidity increases water content but not sugar content, excess water will lessen sugar quantity, excess rain will wash it out and dew will dilute it, cloudy conditions with poor light will also affect it, so the question is what are the favourable conditions for plants to produce the optimum amounts of nectar. I did find this study from 1916 but there must be more recent scientific papers that are readable and pertinent to Ireland, Scotland, Wales and England.

http://lib.dr.iastate.edu/cgi/viewco...ype=additional