The value of cancelled merger deals for this quarter is closing in on the value of deals actually completed and the two measures will draw level if the mammoth takeover of Canadian telecommunications group BCE falls through.

With BHP Billiton dropping its bid for Rio Tinto last week, the dollar value of merger deals cancelled so far this quarter rose to $322bn compared with $362bn in completed M&A transactions, data from Thomson Reuters show. The last time the value of completed deals was so low in comparison with cancelled deals was in the first quarter of 1987, and this quarter could ultimately prove worse.