Seasonality here is absolute: the weeks before each filing date carry the year. Content published two months earlier takes those searches; the same page written during the deadline week works for next year, not this one.
The other half are people starting up. They search with a different vocabulary altogether: company or sole trader, registration steps, first deadlines. They convert more slowly but stay for years if you get them through the first months.
Specialisation is the fastest lever in this sector: accountant for landlords, for hospitality, for contractors, each with a town behind it. The generic term belongs to national portals and software brands and is not worth the fight.
Client-facing services are searched separately too — payroll, VAT, year-end accounts. A page for each of them ranks for its own searches; a single "our services" list ranks for none of them.