Damp starting problems

[3bells]

Hi
Got a W reg 1.4 Polo SE. For some time now, when it is damp I have great difficulty starting. It turns over but just wont start. Normally if I leave it for a few minutes to half hour or so it eventually starts. Then its ok for the rest of the day.
Today however it wont start and I had to take my hubby's car.
I have ordered some spark plugs and hopefully that will make a difference, I don't think they have been changed in a long time.

Has anyone got any other ideas, bearing in mind I am not mechanically minded.
Thanks
Jackie

[3bells]

I forgot to add, that when it is not damp outside starting is ok. It's only when it has been a damp night.