The union representing staff at the Driver and Vehicle Licensing Agency (DVLA) has expressed “deep concern” over the letterbomb attack that left a female worker hospitalised.

The Public and Commercial Services Union (PCS) has called for a risk assessment of post opening in all DVLA offices, as well as an urgent review of postroom security across the Civil Service.

The attack in Swansea yesterday morning is the third of its kind on motoring-related companies this week.

On Tuesday a package exploded at the offices of Vantis, an accountancy firm linked to Speed Check Services, a provider of digital speed cameras to the police.

That followed a letter bomb attack on Monday at the central London offices of outsourcing provider Capita.

Mark Serwotka, PCS general secretary, said: “It is completely unacceptable that people who serve the public have been targeted in such a way and we urge staff across the whole of the civil service to be extra vigilant.

“Working with management to ensure the safety of staff, we are calling for a risk assessment of post opening in all DVLA offices, as well as an urgent review of post room security across the whole Civil Service.”