Complex sentence: During his short tenure as Minister of Finance, Lafontaine was a main bogeyman of UK Eurosceptics, because among other things he had called for the prompt tax harmonisation of the European Union, the result of which would have been an increase in UK taxes.
Split into simpler sentences: During his short tenure as Minister of Finance, Lafontaine was a main bogeyman of UK Eurosceptics. The was because, among other things, he had called for the prompt tax harmonisation of the European Union, which would have resulted in an increase in UK taxes.