In reply to tlm:
The answer to the question in your title is "badly!"
There are quite a number of reasons for this, among the more important are the dramatically increasing length of pension years to working years both due to longer educational periods and longer lifetimes, the very poor investment returns due to exceptionally low interest rates and low stock market returns of recent years and last, the high charges/poor management/restrictive rules applied to the suppliers of private pensions, finally the uniquely (and most who do not get them think utterly unsustainable and unjustified) public sector pensions still set as a % of final salary and years worked (though this is gradually being reigned in as totally unaffordable even in the public sector, it has the population density of the dodo in the private sector).
You do get the state pension as well as private pension, it is based on the number of years that you have contributed to it, up to a current maximum of 30. But there is (or maybe, this is not clear), a catch about the number 30, due to a change that is proposed very soon, it is not clear if the number of qualifying years will effectively rise, as they need to do.
If you work you still keep all your pension, but both your earnings and pensions are taxable.
Why don't you know more about it?
Very few people do, because it is :
1) boring
2) incredibly complicated
3) has layers and layers and layers of complication due to different generations of politicians/economists trying to alternately fix/ignore the problems
4) involves huge amounts of money, but is very poor value for the punter, despite being widely portrayed as the "prudent" thing to do
5) is an incredibly intractable, possibly unsolvable problem, so it is easier to ignore it and pretend that it doesn't exist
6) not many people do know much about it, a lot of those that do have vested interests and axes to grind about it
Post edited at 12:22