You're probably dicing with death if you set up a private pension these days (SIPP) for one reason -
THE GOVERNMENT WILL TRY TO STEAL IT.
Not so much steal though but force you to buy Government bonds + implicate all sorts of new taxes. Governments are running out of cash, in the end they always turn on the people and many people have considerable assets, those assets those in power believe belong to them/the state.
The best advice is to yes, save for your older age, but don't so so within the system. The best way to do this is to buy collectables, whether for £50 or £5,000,000. Collectables can be really anything, ink wells, comics, Picasso's, old mobile phones, stamps, photos etc. Always buy wuality and try not to invest in things that have already gone through the roof as they won't be that good value. It's not going to be easy, nothing is, but when your neighbor is crying that his pension has been stolen, you'll be fine.
Also use ISAs for investing in stocks as money can be withdrawn easily. What to invest in, simple, use the perpetual portfolio' strategy as it will be far better than any investment strategy 99% of professional money managers offer. Use ETFs and don't think, ie always be invested, take the rought with the smooth, there's no way out unless you want to under-perform...