Don't know if it's related to the pen applied thing mentioned in another comment but I just caught up with this from a couple of weeks ago on a mailing list:

"This being notional (sic) insect week I thought I might remind those of you who have shown interest in my insect bite clicker thingie that they are now available in Boot's chemist shops; indeed there are 2 varieties. They are to
be found with the travel stuff or the insect bite creams."