The Glasgow firm, which is run by brothers and major shareholders Douglas and Iain Anderson, achieved an 11% jump in turnover from £157.7 million to £175m in the year to March 31.

And turnover is showing further growth in the new financial year.

GAP Group’s pre-tax profits rose from £15.8m to £17.1m. This pre-tax profit figure has been exceeded by only the £18.6m achieved in the 12 months to March 2015 – a year described by Douglas Anderson as a “purple patch”.

The company had by March 31 this year increased its employee numbers to 1,633, from 1,502 a year earlier. GAP Group employs 462 staff, 28% of its total workforce, in Scotland.

Douglas Anderson highlighted GAP Group’s £4m purchase, in recent weeks, of a five-acre site at Tilbury in Essex, as it continues to expand its footprint in England.

He noted the company’s total investment at Tilbury, including development of the site, would be about £6m.

He told The Herald: “It gives us a real credibility, and an ability to do things other people can’t do. If you want a service around the M25 and in the M25 we need to be there. The cost of servicing transport, in people terms, is just impossible unless you are there.”

Chris Parr, who previously headed paper manufacturer Tullis Russell and joined GAP Group in May last year as financial director, said of the Tilbury investment: “It is something that really differentiates the business. that level of investment, you need a 20 to 25-year view on that. The family ownership allows stability and long-term planning.”

Douglas Anderson noted GAP Group was still the fifth-largest player in its sector in the UK by turnover, with about a 4% share of the plant and tool hire market, while it was in third position in terms of annual pre-tax profits. The company had 134 locations at March 31.

GAP Group chairman Danny O’Neil noted the new divisions launched by the company in recent years, in its expansion beyond traditional plant and tool hire, now accounted for 30 per cent of overall revenues and an even-greater proportion of profit.

Non-mechanical equipment hire, which includes crowd-control barriers, temporary fencing, road plate, and trenching and shoring systems, is among the new divisions. Other new divisions launched since 2010 are welfare services, which hires portable toilet units, and operations supplying surveying and safety, and lifting equipment.

Mr Parr highlighted the fact that GAP Group had increased its workforce by about two-thirds over the last four years, from 995 at March 31, 2013.

Commenting on turnover so far in the new financial year to next March, Mr Parr said: “We are annualising about another 10 per cent growth as things stand.”

Mr O’Neil noted GAP Group invested a further £73m in its hire assets during the year to March. He highlighted GAP Group’s “strategic focus on the less volatile areas of infrastructure and utilities”. Scottish Water is among GAP Group’s customers.

While acknowledging a “very short-term” impact from several major infrastructure projects in Scotland coming to an end, Mr O’Neil said: “It doesn’t seem the dynamics of that are that is going to decline long term.”