Williams, also the chair of the IPA Media Futures Group, was speaking to a House of Lords Communications Committee, which is reviewing the regulation of TV advertising. He said: "If you were to put a number on what could happen (if CRR was removed), it could be price rises in the region of 5 to 10 per cent."
He was giving evidence alongside Tom George, the chief executive of MEC, Andy Jones, the chief executive of Universal McCann, and Geoffrey Russell, the director for media affairs at the IPA.
The House of Lords Communications Committee announced it was to review the regulation of TV advertising in July, two months after the Competition Commission ruled that CRR should stay after its own year-long probe.
George said: "Fundamentally, things haven't changed (since CRR was introduced in 2003). ITV1 is still a very important channel within TV as it is has a unique property in that it is able to build coverage very rapidly."
The Lords also asked questions about the role of media agencies, what benefits they offer clients, and whether it would be viable to replace the current way of trading TV airtime with an online auction.