The Publicis Groupe-owned media agency expects growth of 9.7% – the fastest rate since 1998 when ad growth was 9.8%. Zenith is even more bullish than WPP’s Group M, which last week boosted its UK forecast to 7% growth next year. Jonathan Barnard, the head of forecasting at Zenith, said: "It is pretty stellar -- the fastest growth rate of any mature market."