The standard/most common European chamber length is 65mm. Converting this to "English" it comes out to 2.559". This is very near to 2 9/16"(2.5625"). 2 5/8"(2.625") converts to 66.675mm in metrics. I believe (though could be proved wrong) the vast majority of British, so called 2˝" chambers will in fact measure from 2 9/16" to 2 5/8".

Miller/TN
I Didn't Say Everything I Said, Yogi Berra