In general you will be able to take 25% of the value of your pension pot as a tax-free lump sum.
If the total value of all your pension benefits (excluding the state pension) is below a certain amount - £18,000 in financial year 2012/13 - you will be able to take all of your pension pot as a lump sum; 25% of it will be paid tax free but the rest will be taxed.
If you are in an occupational scheme and have a very small pot in that scheme (under £2000) you will be able to take it as a lump sum even if you have other pension benefits in other schemes. 25% of it will be paid tax free but the rest will be taxed. At the moment this rule only applies if you are in an occupational scheme (i.e. a scheme run by a board of trustees) as different regulations apply to group personal pensions and stakeholder plans.