UBS has jumped up to sixth in the global mergers and acquisitions rankings for the year to date, helped by a single client which accounts for just below 60% of the Swiss bank's deal volume.

The Swiss bank has worked on $249 billion of deals in the year to date, according to preliminary Dealogic data for the first nine months of 2013. Over half of that figure comes from work conducted for a single client: Vodafone.