Best to ask Grow Mayow - the
email on their blog is
Growmayow@gmail.com.
Generally speaking, unrotted manure can be picked up at no cost - for example
from these stables in Mottingham - but you'll need to wait a few months before you can add it into your soil. You can get it delivered for not much more than the cost of transport if you can take a full trailer load - c. 10 cubic meters. I paid £10 for a load to my allotments last year, but this will not be convenient for most gardeners. You also need to barrow it off to wherever you are going to let it rot down. Here's mine earlier this year
#gardeningSE26
If you want it ready rotted down, you can probably also dig into piles at stables, but it will be at the bottom, and other people will have also tried digging it out before you. It also becomes worthwhile for stables themselves to bag it up when rotted, and sell it at a price to reflect the work and time involved - I think Dulwich Riding School do this, but the economics will be similar elsewhere.
Such manure, rotted or not, will contain seeds, so you'll also get some weeds with it.
I'm PM'ing you with the mobile number for Mottingham stables