Problem Serving PHP Pages in Apache userdirs

I thought I had already posted this thread, but can't find it, so apologies if this appears twice.

I am moving from Debian to Ununtu Lucid. I have got PHP working OK on my main virtual servers. However, in userdirs the browser tries to download the file, instead of it being processed by PHP.

I have compared my Ubuntu userdir.conf to the Debian version and can't see the problem. I have changed my root web folder to AllowAll. What other configuration options have I missed?

Ian.