The UK Takeover Panel told Adecco to clarify its position. The firm said it was focused on a recommended deal but was “keeping all its options open”.

MPI last week rejected a 400p-a-share approach as “materially undervaluing” the FTSE 250 company.

It strengthened its case for a higher offer by reporting record half-year figures despite City job losses.

Two-thirds of its profits are earned outside the UK and it delivered a 22 per cent rise to £84.1million on revenues up 26 per cent to £500million.

Chief executive Steve Ingham called the results a “testament to the increased diversification of the group”.

Adecco had made much of wanting to make a friendly approach, he added. “If it is as good as its word, then it will be friendly.”

Broker Kaupthing said  retaining MPI’s top managers was the key to a deal but they were more likely to “walk than work for Adecco” even if run independently. MPI shares rose 25p to 342.50p.