The construction arm was restructured earlier this year following problems with legacy contracts.
A trading update from the firm today said: “New contract wins in UK Construction continue to be achieved on better terms and at improved margins.
“However, the business will incur a loss in the first half of this financial year due to the commercial pressures on many of the older contracts entered into more than eighteen months ago that are now approaching final completion.
“The management of the business is focused on bringing these contracts to finality in the second half.”
Fit-out is performing strongly with ISG currently on site on nine London schemes worth more than £300m.