RIPE IP subnet question

Hi,

Looking at the RIPE database of IP addresses, there is a subnet registered to my business (has our name, address in the descriptions, and was registered by a previous employee). However the maintainer attribute is a different organisation. The subnet is unused, is larger then /24 and has no AS associated with it.

So, hopefully a simple enough question... Is it mine to advertise? And will the maintainer receive a automated email alerting them that a new AS is advertising it?

Thanks.