The DVLA is urging drivers to retake their eye test following concerns that motorists may be driving with dangerously poor eyesight.

By law UK drivers must be able to read a number plate from 20 metres (65ft) away.

But a DVLA survey has suggested that half of UK drivers are unaware of this.

In the survey, 50% of drivers admitted they did not know that a minimum level of vision was required to hold a driving licence, the BBC reports .

Reading a number plate from 20 metres is part of the practical driving test.

Today the DVLA, the government agency which issues driving licences, launched its EYE 735T campaign.

The campaign encourages drivers, who passed their test many years ago, to take an eye test as a person's eyesight deteriorates over time.

Dr Wyn Parry, DVLA’s Senior Doctor, said: "The number plate test is a simple and effective way for people to check their eyesight meets the required standards for driving.

"The easiest and quickest way to do this is to work out what 20 metres looks like at the roadside — this is typically about the length of five cars parked next to each other — and then test yourself on whether you can clearly read the number plate.

"It’s an easy check to perform any time of day at the roadside and takes just a couple of seconds.

"Having good eyesight is essential for safe driving, so it’s really important for drivers to have regular eye tests.

"Eyesight can naturally deteriorate over time so anyone concerned about their eyesight should visit their optician — don’t wait for your next check-up."