are in prison for criticising the official unions. Often the demand for "labour market flexibility" is combined with the demand for strong immigration controls, to block any movement of labour which would be only a burden for capital accumulation. The term "flexibility" is used because, while capital must be able to move freely around the globe, the movement of labour must be strictly controlled. If that control does not exist, it is argued, it could mean additional costs to employers and taxpayers. Criticism It has been argued by Ian Steedman that Marx's own concept of labour power was in truth very similar to that of David Ricardo and Adam Smith and, therefore, that Marx was not saying anything really new. However, Marx's interpretation is (as he himself said) different from the "natural price of labour" of the classical political economists, because the "free play of market forces" does not gravitate spontaneously and automatically toward the "natural price" (the value) of labour power. Precisely because labour power is a unique and peculiar commodity, being lodged in the living worker, it does not conform to all the same laws as other kinds of commodities. Depending on social conditions, labour power may durably trade at prices well above, or below, its real value. Marx only assumed that labour power traded at its value, in order to show that even if that was the case, the worker was still economically exploited. But he was well aware that often labour power did not trade at its value, either because of unfavourable wage-bargaining conditions or because of labour scarcity. A recent criticism by Prof. Marcel van der Linden is as follows: "Marx's thesis is based on two dubious assumptions, namely that labour needs to be offered for sale by the person who is the actual bearer and owner of such labour, and that the person who sells the labour sells nothing else. Why does this have to be the case? Why can labour not be sold by a party other than the bearer? What prevents the person who provides labour (his or her own or that of somebody else) from offering packages combining the labour with labour means? And why can a slave not perform wage labour for his master at the estate of some third party?" This difficulty was first noted in research conducted during the 1980s by Tom Brass, gathered together in his 1999