[ALUG] Strange lack of PHP error reporting

I'm having a real hard time at the moment because for some reason PHP errors (in web pages) don't seem to get reported anywhere. I've narrowed the problem down a bit, if I put a PHP file in my root web directory then any errors *are* reported. However if I put an error into some of the code in my wiki nothing happens except that I get a completely blank page. I've looked at the .htaccess file, no joy there, doesn't set anything relevant. There's nothing appearing in the apache log file either, total silence. Any ideas? -- Chris Green