Dame Martina Milburn, the chair of the Social Mobility Commission, has announced her resignation.

Ms Milburn said that she could no longer commit to chairing the commission as her job as group chief executive of The Prince’s Trust commanded her full attention. 

Background: Dame Martina Milburn backed for Social Mobility Commission

More: Social Mobility Commission admits making little impact

News: More than half of employers stop recruiting apprentices

In a letter to prime minister Boris Johnson, Ms Milburn wrote that she had made the decision “with deep regret, and after several sleepless nights”.

She writes: “I am extremely proud of what has been achieved at the commission in the last two years – appointing the 12 very diverse commissioners, re-establishing the secretariat and commissioning a variety of reports from the state of the nation to an employers’ toolkit. 

“Currently, we have 16 reports in the pipeline, have conducted a popular series of webinars for employers and have begun to form partnerships with bodies such as the metro-mayors and with other important commissions. We have also brought the social mobility charities together and appointed a range of social mobility ambassadors. 

“However, it is not nearly enough and given the strong links between social mobility and poverty I fear this current crisis will only serve to make social mobility harder than ever.”

Education secretary Gavin Williamson wrote to Ms Milburn to personally thank her for her "strong and effective leadership”.