This, however looks fairly promising. I'm in Cheltenham which is pretty close to Glastonbury, and we haven't had any heavy rain for a very long time.
From the METO UK Further Outlook thread.
UK Outlook for Friday 24 Jun 2011 to Friday 8 Jul 2011:
Fairly changeable weather is expected to continue, especially across northern and western parts of the United Kingdom, where showers or rain are most likely. The south and east should see more in the way of drier and brighter conditions but there is still a chance of a little rain at times. Temperatures are likely to remain close to average in most areas, but will probably remain a little below average where any rain persists in the north and west. However, some southern and eastern parts of the UK may continue to see above average temperatures at times.