Found the below from
linkIts dated sometime after June 2003
By way of an example of how workers are disadvantaged, take Mr Smith, who is a water industry consultant. He has had his own UK company, through which he provides his services. He earns £70,000 per year and makes contributions of £10,000 to his UK personal pension plan. Mr Smith sees an opportunity in Germany and moves there, expecting to stay for a few years.
During his time in Europe he makes contributions to the German social security system, but would like to continue paying contributions to his own UK personal pension plan, if he can get tax relief on the contributions. As soon as he goes to work in Germany, he will become a German resident and will cease to be a UK taxpayer. When in Germany, he and his company will become liable to pay social security contributions totalling 19.5% of his salary in Germany to cover pensions and unemployment.
As far as his UK personal pension is concerned, while he can continue to contribute, his payments are limited to £3,600 per annum. However, these contributions are not tax-deductible in Germany, so that he will be pay these contributions out of fully taxed income.
After four years he decides to return to the United Kingdom. His contributions to the German pension scheme are not sufficient to enable him to qualify for a German pension, so Germany will make a refund of his contributions.