A strong recovery in advertising helped bring about a sharp rise in revenues at broadcaster ITV in the third quarter, though growth in ad sales are seen slowing in the fourth quarter.Group revenues climbed by 11% from the same period last year to £1.456bn, with advertising revenues climbing by 16%. Ad revenues are currently forecast to be up by 10% in the fourth quarter.ITV added that external revenues from studios are down by 10% to £205m 'emphasising the need for creative renewal.' The company has been focused on cash and costs helping to reduce net debt to £366m on 30 September from £437m on 30 June. 'The television advertising market has continued to recover strongly,' chief executive Adam Crozier said.'However, this does not disguise the significant challenges ITV faces and we remain focused on delivering the five-year Transformation Plan.'He pointed to HD versions of ITV2, ITV3 and ITV4 and new deals for the talent shows X Factor and Britain's Got Talent.'The economic outlook for 2011 is uncertain and we continue to plan on a cautious basis,' he said.