It starts with a look at what you actually have — machines, network, email, backups, who has access to what. That list normally does not exist, and creating it is where most of the quick wins turn up.
Then day-to-day: things that break get fixed, remotely where possible and on-site when it needs hands. £45 an hour, no call-out charge in Luton, and no obligation to sign anything.
Alongside that, the work that stops calls happening — networks that hold up, backups that are tested, patches applied, and a security review that is honest about what is exposed.
You are dealing with one person, formally qualified rather than self-taught, with the certifications listed on the IT support page. The upside is that nothing gets passed between departments. The limit is that this is not a 24/7 helpdesk, and if that is what you need you should have one.