Gatwick has two 'Bag Drop' options:
1.Bag-Drop is open from 05:00 on the day of departure for all passengers.
or
2.Early check-in is available. You can check-in bags between 16.00 and 22.00 if travelling on a BA flight that departs before 15.15 the following day.
Full details can be found here: http://www.britishairways.com/en-gb/...london-gatwick