Wiebke, that's interesting! So for UK farmers, meadow grass is the same as orchard grass, i.e. dactylis glomerata and nothing else?
From what I've read, in the US, meadow and orchard are two distinct hay varieties. For example, Oxbow has two separate products: Orchard grass (which they advertise to be single-species hay) and Meadow hay (which is a mixed hay: 'Organic Meadow Hay is composed of a variety of naturally occurring grass hays providing an enticing combination of textures, fragrances and flavors.') I'm also reading the following two websites and arriving at the same conclusion: in the US, meadow hay is a mixed hay as opposed to timothy and orchardgrass:
http://animals.mom.me/difference-between-timothy-hay-meadow-hay-rabbits-6461.html and
A Brief Guide to Meadow Hay for Guinea Pigs - Online Guinea Pig Care. I do however strongly disagree with the conclusion that meadow hay, being generic, is inferior to timothy and orchard.
In any case, thanks for the information, I certainly didn't know that in the UK, the terminology is different. In that case, I could get in touch with some British meadow hay providers online, and problem solved

I think read excellent reviews on Dean's Meadow hay, so I may try it.