Your registration, as the first thing they read
NICEIC or NAPIT, and Part P, set as real text at the top of the page and in the footer, with the number a careful customer can check against the register. In your trade the registration is the whole sale, so it is not tucked into a badge image at the bottom.
A number for the fault, a form for the date
On a phone the number is first and dials in one tap. Under it, a form for the work that is booked rather than begged for: what the job is, the postcode, and the date it needs doing by, so an EICR request arrives with the deadline already on it.
A page for each job people search by name
EICR, fuse box replacement, EV charger installation: each is its own search and gets its own page, saying what it involves, what it costs from, and what you hand over at the end. The certificate the customer needs is named on the page, because it is the thing they are actually buying.
A page that loads before they go back to the results
Under a second on a mid-range phone. Somebody standing in a dark hallway does not wait for a hero image, and the second name on the list gets rung while the first is still loading.