I am looking for "pick and pack" fulfillment companies in the UK who
are oriented towards small businesses (i.e. no minimum volume or
storage amount, a low or zero monthly fee, just per-item
storage fees), have a web-based inventory management system and
publish their prices upfront on the web.  Please can you find 2 or
more such companies. Thanks.

N.b. I don't need credit card processing, order helplines for customers etc
-- just that they ship from an inventory of stock that I supply
according to a daily order file that I send them.

Try http://www.pickpackanddispatch.org.uk/

Hope that helps