Well I'm an idiot - the fulltext index on page_text was missing from a default installation. It didn't break searches but probably slowed them down tremendously. Also set engine to MyISAM on page_text to avoid cryptic error messages from MySQL.

// UK lang variables

tinyMCE.addToLang('',{
directionality_ltr_desc : 'Direction left to right',
directionality_rtl_desc : 'Direction right to left'
});