Constructionline director Simon Kellaway said he was delighted by his firm's increased popularity.
However, the Association of Consulting Engineers says that its members are still concerned about the effectiveness of Constructionline.
A year ago, a survey of ACE members revealed widespread discontent with the service and warned that it could withdraw support.
Robert Osborne, ACE acting chief executive, said he supported the principles that underpinned Constructionline and remained committed to reducing the number of tender forms consultants were required to complete to work in the public sector.
But he added: "It is clear that Constructionline has yet to achieve this aim."