If you look at: http://www.metoffice.gov.uk/weather/uk/uk_...st_weather.html and then click on the 16 to 30 day forecast you are told:

UK Outlook for Friday 18 Jun 2010 to Friday 2 Jul 2010:


The somewhat unsettled theme with sunshine and showers is likely to continue at first. However, there are indications that there may be a trend towards higher pressure giving drier, brighter and warmer conditions with some sunnier parts perhaps very warm. Southern and western parts may see more in the way of rainfall with the possibility of some thundery weather, whilst northern and eastern regions should remain drier.


Updated: 1226 on Thu 3 Jun 2010

Not looking too good eh?

Well the higher pressure is what we really have to hope for. I can't give you a figure for what sort of level of pressure we will be looking for then - as the term high pressure is just relative to whatever the pressure was in the days before you take the reading.

The outlook for thundery showers isn't really something that should shock us looking back at weather this time of year in previous years, also considering the European Monsoon season: http://en.wikipedia.org/wiki/Monsoon#Europe

All we could do is as Glastonbury Festivals to either move the date of the festival into July when the weather is more settled, or more the festival East - where we won't be so affected by the cool, damp air and low pressure coming off the Atlantic.

But as said before, don't worry just yet, a hell of a lot can and will change between now and June 23rd (19 days and counting...)