I think the best way to tackle this would be to set out an online induction for site, factoring in a three strike system (or system of some sought), full information on current guidance obviously trimmed down to certain areas and a disclaimer to the employers discretion if rules are not being adhered to. This being for all that come to site.In terms of the knowing, I've been very lucky over the years that I've worked with very honest people in the industry. I feel like the trust between everyone on build would be fine.
However from a staff point of view when live, I feel it may be worth having publicly visual hand washing stations (ex. rather than underneath the front of a bar, having a wash station on a back bar), for piece of mind and for fellow staff members to encourage/remind each other. Factoring something like this in the induction, that we are all looking out for one another and in this together.
Knowing that everyone working on site are working to covid standards set by h&s.
Knowing that PPE is provided buy employer.
To know the employer has a run through h&s with every single member of staff on site
If staff members do not comply they are spoken to or walked off