The group said it expects pre-tax profits to come in at between £535m and £555m for the full year, compared with previous forecasts of £614m.
Capita blamed a slowdown in “specific trading businesses”, one-off costs incurred on a Transport for London (TfL) congestion charging contract and “continued delays in client decision-making”.
The firm added: “As referenced at our first-half results, our Asset Services division has seen less activity in the short term, following the EU referendum.”
Delays have dogged the TfL IT contract, and Capita expects to incur up to £25m in one-off costs as a result.
Capita also said it is in a contractual dispute with Co-op Bank regarding “obligations relating to the transformation of services”, flagging that there is a “risk of litigation”.
Capita reassured investors that it is taking immediate steps to reduce the cost base at its under-performing businesses, which will give the company a boost next year.