Even though this article by Rebekah Mintzer reports on a survey of U.S. in-housers, I suspect their U.K. counterparts would give similar answers.

Of my colleagues who were in-house with me 20 years ago, those who have left the legal profession have gone on to become CEOs which accords with the survey results.

Whilst being an in-house lawyer is a great career, some will naturally move into business itself, driven by an entrepreneurial flare. There's many ways an in-house lawyer can do this. For example, one woman I know moved from being a team leader in a large in-house legal department to becoming the Executive Assistant to the General Counsel. Once she was moving within the elite C-Suite (as the Americans call it) she became known to the CEO who, after a couple of years, gave her the chance to run a business division. She fulfilled that role very successfully for several years before being headhunted to be the CEO of an exciting private equity owned business. The key to her advancement was the fact she had developed a good relationship with her General Counsel and he thought of her when he decided he needed an Executive Assistant.