Kelvin Hughes
Or go to an art shop and get a Rotring pen. This is the right tool, but if they are not used regularly they gum up, and they are pricey.
WH Smiths should stock Pritt-Stick for the blocks!
I use an Edding 2189 or 2185 pen. The width (0.7mm) is a tiny bit wider than I'd like but not so much so as to be a problem. Buy them from Staples or Rymans etc.