From what I've read so far, if you are a UK resident for tax purposes and you receive a lump sum from your superannuation (pension) fund then the Inland Revenue regard it as an unauthorised payment which will be taxed at 55%. I am in the process of finding out myself exactly how it will affect myself and I would advise others, especially if you have $600,000 to consider, to find out for themselves. Get professional advice or contact the Inland Revenue yourself is my advice.
My plans are on hold until I know exactly where I stand as 55% is an eye watering amount to pay on top of the 15% tax paid putting it in.