Safe deposit range
10–15% mobilisation deposit is London 2026 standard for projects £50,000+. Covers: insurance bond fees, materials ordered with lead time (windows 8–12 weeks, kitchens 6–10 weeks, steels 2–4 weeks), site set-up (scaffolding hire deposit, skip hire, hoardings). Deposit should equal the value of work/materials secured in the first 2 weeks. Anything above 20% suggests builder is using your money to cashflow other jobs — major red flag.
Protection mechanisms
Credit card (Section 75 protection): purchases £100–£30,000 by credit card are jointly liable on the card provider if builder fails to deliver. Builder may resist (1.5–2.5% surcharge); negotiate to split — first £30,000 on card, balance by bank transfer. FMB/TrustMark insurance-backed warranties: cover deposit and works if builder goes insolvent (FMB Insurance Backed Guarantee £150–£500 cost). Materials-on-site invoices: require builder to send invoices showing where deposit went (window supplier, steel fabricator).
When to be most cautious
Builder is new to you (no prior project history). Builder pressures fast deposit before contract signed. Builder asks for cash payment with no invoice. Builder asks for >25% deposit. Builder isn't FMB, TrustMark, or insurance-backed. In all these cases — slow down, get JCT contract signed first, never pay before contract.
