It depends on how far you are prepared to travel from the Midlands. You might just need to travel out quite a bit to get value for money.
There are a few summer jazz courses and the odd wknd but rarely one day. The ones that spring to mind are http://www.jazzacademy.co.uk/academy.htm
in Tunbridge Wells and http://www.musicforyousummerschools.co.uk/jazz.htm
. Trinity College of Music are also doing a summer course http://www.trinitysummerschool.co.uk
. Then there is the popular http://www.mehrclef.com
Dont forget the very expensive but apparently worth every penny Jamey Aebersold summer course http://www.jazzwise.com
Morley College in London do regular evening and occasional wknd classes http://www.morleycollege.ac.uk
. the amazing Tim Richards teaches there with Sara Dhillon, equally brilliant.
There are also some European ones that can be part of your summer hols. The ones that Spring to mind are the Umbria jazz clinic in Italy http://www.umbriajazz.com/clinics
and I think there is a popular one in France http://www.jazzsummerschool.com/french_jazz_school/index.htm
, also do one to Cuba.
None are advertised at the price of Â£5 I'm afraid