Is It Illegal to Work in Security Without an SIA Licence?

It depends on the role - for most security work, yes, but there's a significant exception for in-house staff.

If you're employed directly by the company you're protecting, rather than supplied by a security contractor, you generally don't need an SIA licence at all - GOV.UK confirms this in-house exemption directly. The main carve-outs from that exemption are door supervision and vehicle immobilisation, which require a licence regardless of who employs the guard.

For contracted security, working without the correct licence for that specific activity is a criminal offence, risking prosecution for both the individual and the company that deployed them. In short, yes - an SIA licence is a legal requirement for most contracted security work.

Licensing confirms someone's been vetted and trained to a baseline. It says nothing about how they'll actually handle a real incident - that's what proper conflict management training is for.