The firm’s board said the bid fell significantly short of its recent revaluation of the portfolio and did not reflect the extra value the investment team brought to Balfour’s construction and services businesses.

In the summer, directors re-rated the PPP portfolio value by 46% to £1,051m with 37 UK contracts upped by 63% to £801m.

The re-valuing followed the sale of stakes in its Durham hospital PFI and Knowsley Building Schools for the Future project for £97m, exceeding previous valuations.

Now Balfour said it expected the portfolio to be worth more than this latest estimate.

“This has been recently evidenced by the disposal of an investment at a 28% premium to the half-year directors’ valuation,” said Balfour this morning.

It will publish the latest estimate with KPMG’s review of construction projects, which is now being pushed back a month to December.

Balfour said the report with recommendations to the board will now be published in late January.

Its rejection statement said: “The strategic value and synergies from owning the current investments business – both the PPP portfolio itself and the skilled team that operates and develops the business – is material to the Balfour Beatty group as a whole.

“The group’s construction and support services businesses derive real value from the investments business, something which needs to be taken into account in valuing the group as a whole, and in evaluating any proposal to acquire the Investments portfolio or business alone.”