Who you are (Name, NI Number, Address, Tel, Smoker/Non Smoker)
Skill Set – some people (especially IT, prefer you to rate your abilities in each area)
Most recent job (date to - from)
Brief outline of role and responsibilities
Any added value, benefits, budget saved, delivered early
I'd not put on ni number (why do they need to know?), and why do they want to know if I smoke?
At the top, be really clear about your skills. Bullet points, that make it obvious - for example don't say 'good leadership skills', put 'x years team management'.
On the rest - I always try and think of one thing per job that sounds impressive - for example one of my development jobs I say something along the lines of 'specified and developed a major feature of their flagship product blah'. If you managed people in any of your jobs, make sure you're clear about that.
I always have a small bit about personal stuff that lists various exercise things including mountain unicycling. Putting something odd on there gets me remembered by them, and guarantees an easy to answer question in the interview (I don't think I've ever not been asked about that). I've never had any problems about it being dangerous.
I don't list GCSEs since I got A-Levels / university degree / some experience. To be honest I can't remember if I even listed A-levels last time. Although you do see CVs where they listed their Grade 2 piano exam etc. so obviously everyone has a different approach to this.