Collect pens as they stop working (biros, felt tips, ink erasers, fountain pens, highlighters, marker pens PLUS tippex bottles and plastic-propelling pencils) and either drop them off at a local Terracycle collection point or take them to your local Ryman stationery shop - there branches are listed here.
Bic (the biro-making company) is funding the pen collections (any brand of pen is accepted), which includes these advertising posters (scroll to the bottom of the page) on the Terracycle website - so get your workplace and local school(s) involved, as well as your household!