The world's biggest maker of airport scanners posted lower profits after the pound's strength compounded "disappointing" trading at its X-rays unit.

Engineering conglomerate Smiths said the detection business, which makes sensors that detect explosives, chemical agents and biohazards, saw sales fall 5% or £25 million as national governments cut their budgets.

The division also had to contend with a further £22 million impact from foreign exchange translation as profits in detection dropped 58% to £25 million.

Smith, which recently celebrated 100 years as a stock market listed company, makes components for products ranging from car paint spray guns to emergency ventilators used by paramedics.

It has faced mixed fortunes as its two divisions serving the healthcare and defence and security sectors have continued to experience tough trading.

This has been offset by progress at John Crane, which serves customers such as oil giant Shell with products including seals and filtration systems, and at Flex-Tek, which provides hosing and rigid tubing for fuel and hydraulic applications on commercial and military aircraft.

It added that declines at its medical unit and the strength of sterling, which cost it £43 million overall, meant pre-tax profits slumped 24% to £302 million.