### Clue: Scientist returned vehicle to policeman (5)
### Answer: DIRAC 
 ### Explanation: Definition: Scientist
 **Reversal of**(returned) CAR(a engine-driven vehicle) **placed after**(to, in an across clue) DI(abbrev. for a detective inspector).
Answer: Paul, English scientist, a leading figure in the field of particle physics, specifically quantum mechanics and quantum electrodynamics.