What must a UK company file each year?
At a minimum: an annual confirmation statement (Companies House), annual accounts (Companies House), and a Corporation Tax return (HMRC). If VAT-registered, quarterly VAT returns via Making Tax Digital. If employing anyone, PAYE and pension filings.
What happens if I miss a filing?
Automatic financial penalties from Companies House and HMRC, potential strike-off proceedings against the company, and personal fines or disqualification for directors. Fixing a strike-off notice is expensive; prevention is straightforward.