London behaves less like one market than like many overlapping ones. A search for a dentist, a solicitor or an electrician returns map results drawn mostly from businesses close to the person searching, so a firm in Wimbledon and a firm in Walthamstow are rarely fighting for the same customer, even though both are in London and both might describe themselves that way.
That has three practical consequences. First, your Google Business Profile needs to sit at a real address where you serve customers, or be set up as a service-area business with the address hidden. Google's guidelines do not allow a profile at a mail-forwarding address, or at a virtual office unless it is staffed during business hours, and addresses of that kind are common in London. Second, each area page needs to be genuinely about that area: which services you offer there, how appointments or call-outs work, and anything that differs, rather than one page copied with the borough name swapped. Third, your name, phone number and opening hours need to agree on your site, your profile and the directories, because conflicting details weaken all of them.
Businesses that sell across the whole city, or nationally from a London base, face a different problem. For them the place matters less and the subject matters more. The work is mostly technical and content, aimed at the specific services buyers search for, with London named where it helps the reader rather than repeated in every heading.
The common mistake in both cases is the same: treating London as a single word to rank for. Most of the enquiries are in the detail, the neighbourhood, the specific service and the question a buyer asks before they pick up the phone.