Physical trade risk plus two exposures unique to surveillance: systems that fail to record, and cameras capturing personal data under UK GDPR.
Insure the trade risk like any electrician – then add what makes CCTV different: professional indemnity for systems that fail to do their job, and clarity on data-protection exposure if you advise on or handle footage. Declare commercial and height work honestly, and keep your tools conditions realistic. The whole package costs less than one camera install pays.