Your level of risk really depends on your appetite for risk (obvious) but also your current age, and projected age of retirement. The idea being the fund(s) you invest in should become less risky the closer you get to retirement.
Depending on your financial position, most people don't realise that you'll be paying 60% tax for earnings between £100k and £125k, as you loose £1 of your personal tax relief for every £2 over £100k. Using a pension deducted at source to bring down your taxable income really helps if your yearly income falls into this bracket.