The Bury-based group revealed that the main UK structural business William Hare enjoyed a 10% sales rise to £158m last year.
But poor operating margin saw pre-tax profit edge up to just £1.2m in 2017 from £830,000 in the previous year.
The firm’s operating margin stood at around 1% despite a strong pipeline of major projects in London.
Across the wider group, which also takes in operations in the Middle East, India and Far East, sales slipped back slightly to £204m, generating a £3.2m pre-tax profit.
David Hodgkiss, William Hare Group’s CEO, said that demand in the UK remained encouraging and was expected to remain stable in the short to medium term.
Hare’s London projects include the 40-storey skyscraper at 100 Bishopsgate, 1 Bank Street for Canary Wharf and 100 Liverpool Street at Broadgate.
The separate Cellbeam business saw sales slide by nearly a third to £13m with pre-tax profit just above breakeven. William Hare Painting held steady at £4m.
Over the year the average number of staff fell from 680 to 504 at William Hare, while total UK headcount was up slightly at 704, and the international activities employed nearly 1,000 staff.