I'm assuming (because all it says is...) public sector top ups - the staff pay extra contributions and the government adds a bit more to it. The whole thing is a bit of a mess though to be fair.
Its a decent breakdown for the most part, and it's good to see, but there's definitely some agendas being pushed in places. It's not really "transparent" because it doesn't break down what they class as "welfare". The fact that you, and many others, associate it with the unemployed buying TVs with it shows as much (that sounds cattier than its meant to, sorry). If it were really transparent then it would state that around 6% of your contributions go towards family, children and social inclusion benefits and the rest is disability, housing, old age support and social services.
This is an interesting blog on it if you're interested;
http://commonslibraryblog.com/2014/11/04/hmrcs-new-annual-tax-summary-whats-in-welfare/