Unions representing Reuters staff in the UK, US and Canada have expressed “deep concerns” about Thomson’s £8bn bid in a letter to the Reuters Founders Share Company, the body which could decide whether the bid succeeds.

The influential group, chaired by Swedish industrialist Pehr Gyllenhammar, is expected to meet this week. Although Mr Gyllenhammar has said its “golden share” in Reuters is “not a poison pill”, it could block any bid it considers would jeopardise the integrity and independence of the company’s news wire service.