In fact, the mathematics are far more complicated. This is because neither all 'big' states, nor all 'small' ones, have the same number of votes. Of the 'big' states, France, Germany, Italy and the UK have 10 each, while Spain has eight. Of the 'small', Belgium, Greece, the Netherlands and Portugal have five, Austria and Sweden will have four, Denmark, Finland, Ireland and Norway have (or will have) three, and Luxembourg has two.
At present, Britain can assemble 23 votes (a blocking minority) with two allies (eg Germany and Denmark), but might sometimes need three. If, for example, its 'big' ally is Spain - only eight votes - then the addition of Denmark, with only three, will not be enough to reach the 23 needed, and the help of a fourth country would be required.
What the UK is now worried about is that pushing up the threshold to 27 for a blocking minority could sometimes require it to find not a maximum of three allies - as reporting of the issue suggests - but four. Britain (10) allied with Germany, (10), Denmark (3) and Norway (3) would still only produce 26 votes, and a fifth country would then be needed to arrive at the figure of 27.
The issue, then, is not how many votes should be needed to produce a blocking minority, but how many countries. The UK's intransigence is based on its concern that some of the countries it sees as its natural allies - principally the Scandinavians - are too weak in terms of votes to help it reach the magic 27.
This concern - whether justified or not - could be largely met by raising the threshold from 23 to 26 votes. Such a compromise would permit Britain to be reasonab1y sure of being able to block legislation with the help of three other countries, rather than four - a reasonable target in an enlarged EU with 16 members instead of 12.