The official language of Gibraltar is English, so yes, staff should be able to speak it fluently. Guests to Gibraltar will expect to be able to converse in English. Obviously when employing someone, especially someone who is public-facing, businesses should take this into account and employ those who can speak English first and any other languages second.
Sometimes you may have a candidate who has no official qualifications in English but can speak the language very well, and some times you have the opposite; someone with qualifications but can not speak English at all. It is important that they can understand and communicate in English easily and fluently.
The GFSB is here to help and support local businesses, we have been offering subsidised language courses for years and we will continue to do so, in order to help the business community offer the best customer service it can.