The FTSE 250 company said in a statement that the profit from the sale is expected to be £32mln and the proceeds will be used to pay down borrowings in 2018.
Last week, Balfour Beatty sold a 12.5% stake in Connect Plus for £103mln. As a result of both sales, the company expects profit-before-tax and year-end-net-cash in 2017 will be above those included in its trading update on 12 December 2017.
"Taking account of both transactions, the expected 2017 Infrastructure Investments profit on disposal is now £85mln. The year-end net cash, which was originally forecast to be in line with prior year, is still expected to be around £103mln higher since the proceeds from the sale of the 7.5% tranche will not be received until 2018," the company said.
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"Arrangements with funds managed by Equitix and Dalmore covering the potential disposal of an additional 5 percent interest in Connect Plus remain in place. These arrangements lapse on 13 May 2018 and are subject to a number of conditions. Therefore there is no certainty that there will be any subsequent transaction," it added.
Following the latest sale, Balfour Beatty has a 20% stake in Connect Plus.