Springbridge

https://www.springbridge.co.uk/bulk-bags/composts/spent-mushroom-compost-standard

Grow bigger, tastier vegetables naturally with this superb mushroom compost. Often called ‘spent mushroom compost’ it’s made originally from a traditional mix of stable and chicken manure - well rotted down - and has already served time pushing up your breakfast mushrooms. Now it’s ready to give up its other nutrients to your vegetables and enrich their natural flavours and colours.

CPA - Horticulture

https://www.cpa-horticulture.co.uk/compost/mushroomcompost?

CPA Horticulture's mushroom compost is composed of composted agricultural straw and rotted manure, resulting in compost that is easy to crumble, spread and work with. Thanks to the compost's chemical and physical composition, it is perfect for improving the texture of heavy clay soils or adding humus to nutrient-deficient soils. What's more, our compost is fully steam sterilised before leaving the mushroom farm.

Mr Muck's

https://www.mrmuck.co.uk/collections/manures-composts/products/mushroom-compost

Mr Mucks Mushroom Compost is a mix of chicken and horse manure with wheat straw. Not only is our mushroom compost an exceptional soil conditioner, but it is also very economical to use on a large scale. It will improve the structure of heavy clay soils, add humus to thin sandy or chalky soils, enrich all soils and supply nutrients for the healthy growth of plants.