
The
Dobermann Club's land at Digswell in Hertfordshire?
Not central UK, but meets other criteria nicely if you were stuck -
Bradfield Village Hall near Reading. Very cheap and huge amounts of outside space if weather is kind to you, no problem with dogs in the hall if it's not. As long as you put prominent signs up, it's easy enough to find, but you do need to do this.
Good luck with it - venues are a nightmare these days, and your date is right in the busiest period.
M.