could be too much water if it fine put them outside for a few hours to see if that helps.

thanks Kennyboy i will try that

Glynis, if they're busy lizzies, they need to be kept between 60 and 70 deg F to germinate - usual practice is to place a sheet of glass or plastic over the trays, which you need to remove and wipe clear of moisture every day.
Mildew on the top means they're very wet and there's no airflow. Best cover would be the raised, clear lids for seed trays - these aren't a tight fit so don't thoroughly exclude air, and collect less moisture.