Yes - it is a requirement of the Regulatory Reform (Fire Safety) Order (RRFSO) legislation to ensure that your Fire Protection equipment is maintained by a competent person. You must have a contract in place to ensure faults can be discovered, attended to and rectified in a timely manner. As for the frequency, it's British Standards recommended to have your fire alarm system serviced by a competent person at least twice a year (sometimes four times a year in special circumstances).