Treat as urgent. Causes include a leaking fuel line, perished filler hose, faulty EVAP system, or a leaking injector seal. Fuel leaks risk fire.
Here's a quick, honest answer from a working UK mechanic — what causes it, what it costs to fix, and what to do next.
Can I drive it? — Only the shortest distance to a garage, with windows open. Better to call a recovery service if the smell is strong.
Could it be a faulty fuel cap? — Yes — a worn seal lets vapour escape and triggers EVAP codes. £15–£40 to replace.