Why do i sometimes get clutch 'rub' when engaging first gear?

Only happens sometimes and only with first gear. If i engage nice and slowly it's fine but if i need a quick get away i experience a rubbing sensation through the pedal.

Ford Fiesta Zetec S. Mk6 '56.
27000 miles.

Might need the clutch fluid topping up or bleeding the system, or the slave cylinder could be leaking. Try pumping the clutch pedal a few times before putting it in gear.

By "rub'. Do you mean a kind of chattering feeling? Do you ride the clutch a lot, or let it slip? Not many miles on car, so I'm guessing the clutch disc is glazed from excess friction. Clutch needs to be engaged or disengaged ONLY, not used as a brake. Live with it, learn to operate manual transmission correctly, hopefully your next clutch will last longer.