The e-learning programme is founded on the basic and practical principle that the use of the internet as a learning tool not only creates anonymity and thus dismantles the psychological barriers that prevent illiterate adults from resuming their studies but also enables them to balance their work, family and learning commitments by learning at home at whatever time is suitable to them.

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For many scientists, however, it is the principle that counts, not the practical engineering.

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While Jackson and his successors framed economic policy as a matter of limited-government principle, Howe argues that the practical difference was that the Whigs sought to create a coherent national transportation system, while Jackson preferred to dole out projects on an ad-hoc basis to individual states.

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While committing itself to the principle of providing accurate information to consumers, the government has warned that there are "real practical difficulties in establishing traceability to identity method of slaughter to the point of consumption".

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One reason perhaps is that although the Russians seem to be keen on such a regime, the US has not elicited enough concessions in principle on law enforcement to make this worthwhile from their perspective (notwithstanding the probable lack of practical effect of such an agreement also).

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"I don't think the practical side has been really thought through ... the devil is in the detail, not in the principle, " he told BBC Radio 4's World at One programme.

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The aides told me they weren't going to stand on principle, that they would have to get a practical way for a recount.

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