The code has been drawn up by executive recruitment firms and the Davies Steering Group. To gain accreditation under the new code companies will have to show that they have taken several steps towards gender diversity on boards.
These include supporting the appointment of at least four women to FTSE 100 or FTSE 250 boards over the past year and supporting women in achieving their first FTSE 350 board membership.
The new code is an advancement of 2011's standard voluntary code. More than 70 executive search firms signed up to the original agreement, including Penna and Oakleaf Partnership.
Oafleak Partnership CEO Nicola Grimshaw told HR magazine the company does everything it can "to provide diverse shortlists", but that real change will only come from within boards themselves.
"Better organisational governance and education is the key to increasing appointments," she said. "I'm not sure how much difference this change will make."
Kathryn Nawrockyi, Opportunity Now director at Business in the Community, told HR magazine she "fully welcomes" the launch, but warned that companies must still focus on their internal recruitment strategies.
“A more equal representation of women in executive directorships will be a signal that these companies have robust talent pipelines that aren’t leaking female talent and are ensuring women are progressing to the internal feeder pool," she said.
Vince Cable called on recruiters to "show their commitment to this work by embracing this new enhanced code”.
"Executive search firms are crucial to achieving gender diversity in both executive and non-executive roles," he said. “Now that all FTSE 100 boards have at least one woman serving on them, and all key stakeholders have embraced the gender diversity agenda, we are confident that with sustained and continued action, we will meet the target of 25% women on FTSE 100 boards by 2015."