No, but there is a limit to the size of a pension fund people can build up tax free. This is known as the "Lifetime Allowance" (LTA) and has been set at £1.5 million in tax year 2012/13. Anything above this will be taxed quite steeply.
If you are lucky enough to be in this position then you should take specialist advice. There is more information on the HMRC website here.
