Before reversing, you should always check that...

Correct answer

it can be done without causing danger to other road users.

Establish that reversing is permitted and safe with the necessary visibility, space and time, including getting out or following another person’s guidance if needed. Reverse slowly and with utmost care. Signal using a reversing light if fitted; otherwise extend the arm horizontally with the palm facing back. Insufficient visibility does not itself change this signalling rule: it requires establishing safety. Stop promptly when safety requires and abandon the manoeuvre if necessary. The 15-metre limit applies to specified supplementary manoeuvres, not every reverse.