Head of health, Unison ▲13

It’s a good job Karen Jennings knows how to rise to a challenge as she may be about to face her toughest yet.

She’s well known in the NHS, where she represents more than 400,000 members. She’s also been active in the Labour party for 25 years and stood unsuccessfully as a candidate for Hornsey and Wood Green in the 2010 election.

Despite this, she is not beyond criticising Labour policies. Unison was implacably opposed to both foundation trusts and the creation of social enterprises to run NHS community services and ran a concerted - and some would argue largely successful - campaign to stop the latter.

Now Ms Jennings is battling the coalition government’s NHS reforms, which she views as leading to privatisation and the end of a universal service. Her tactics are likely to be based on a mixture of mass mobilisation and legal challenges, presenting Unison as the voice of the people who work in the NHS and the public who use it.