I am building a desk with a cupboard underneath to house a computer. I
will need to bring cables through the chipboard desk top. Drilling a
three inch hole isn't a problem but I need something to tidy it up.
Our desks at the office have a sort of plastic grommet for that purpose
with a sliding bit to close the hole after you have put the cables
through.

Anybody know where I can buy such a thing?

Dvae