I dumped the drosera in water for a couple of days. These have now been taken 
out, and I'm waiting a day or so to see if there's any activity.
I had to carry my sarracenia in the same box as the drosera (250 miles
by train - including the infamous Underground across London), so its not
that surprising that they have a small infestation.  So far, I've been
picking them off by hand.  I went to a garden centre this morning, and
about all they had was Pyretheum.  None of the other insecticides had
their active ingredients listed!  I thought there were laws about that
in the UK (there should be).  Anyway I recognised pyretheum as being a
"natural" insecticide - so far I've only sprayed it on one pitcher (with
a nice family of green splodges ("kids") & aphids).  Have people tried
pyretheum?  Is it safe on drosera and sarracenia? 
Thanks for the help so far, folks,
Richard