A good risk assessment is one that professionals and 'competant persons' deam to be "Suitable and Suficient" and reduces risk "As far as is reasonably practicable".
Now while all this is a foreign language to most people and a language specific to Health & Safety Professionals it is required under law (Management of Health & Safety at Work Regulations1999) that they are carried out. They can be "generic" and therefore not worth the paper they are written on or they can be effective and monitored which will make them compliant. They have to be written and inspected by a 'Competent Person' and regularly updated.
Failure to carry out this exersise will be regarded as a breach of the law and is punishable by either a Fine of up to £20,000 or a 6 month custodial term within a magistrates court, or, up to 2 years custodial sentance or an unlimited fine within a Crown Court. The court will need to prove "Negligence" on your part, but if you don't have the preparatory documents to prove otherwise, then you will have no defence.
You as the Company owner or Director have a Duty of Care to protect your Employees, Sub-Contractors and Visitors to your offices, places of work and work sites.
Failure to understand or be aware of the law is no defence. You are obliged to provide effective health & safety advice and guidane to your team.