Complex sentence: In 1979 he took advantage of the end of capital controls made by Margaret Thatcher during her first month in power, which made it legal to take money out of the country without it being taxed or subject to any financial controls by the UK government.
Split into simpler sentences: In 1979 he took advantage of the end of capital controls made by Margaret Thatcher during her first month in power. The change in the law made it legal to take money out of the country without it being taxed or subject to any financial controls by the UK government.