The goodwill balance was created on the following acquisitions:

On the Fisher Engineering acquisition in 200747,980
On the Atlas Ward acquisition in 20056,571
On the Watson Steel Structures acquisition in 2001161

All of the acquisitions above are included in one reported segment (construction contracts) and the cash flows of the businesses are closely related. Testing for impairment is performed at the operating segment level, which is the level at which management monitors goodwill for internal purposes.

The Group tests goodwill annually for impairment, or more frequently if there are indications that goodwill may be impaired.

The recoverable amounts of goodwill are determined from value in use calculations. The key assumptions for the value in use calculations are those regarding the discount rates, growth rates and expected changes to selling prices and direct costs during the year. The directors estimate discount rates using pre-tax rates that reflect current market assessments of the time value of money and the risks specific to the CGUs. Changes in selling prices and direct costs are based on past practices and expectations on future changes in the market.

The Group prepares forecast cash flows based on the following year's budget, approved by the directors, together with cash flows based on projections for the following two years which are derived from the Group's strategic plan. After this period, cash flows have been extrapolated using a growth rate of 1.5 per cent (2016: 1.5 per cent) which does not exceed the long-term growth rate for the relevant markets. The cash flow forecasts have been discounted using a pre-tax discount rate of 10 per cent (2016: 10 per cent).

Following the impairment reviews performed by the Group, no impairment charge was recorded in the year ended 31 March 2017.

Management has run a number of sensitivities when performing the impairment reviews, including a reduction in operating margin and an increased discount rate. None of those scenarios resulted in an impairment to goodwill. Management considers that no reasonably possible change in the key assumptions would cause the goodwill to fall below its carrying value at 31 March 2017.