The Jamill recipe says an extra fine crush of the roasted barley is needed to achieve the true Beamish taste. I used to get my barley double crushed by CML. Unfortunately, CML no longer sell bespoke AG kits.
If you crush your own grain, then double crush. If ordered, ask for it. If they won't do that for you, ask for the barley to be bagged separately and use a rolling pin to crush it. Jamill mentions using a coffee grinder as another method but I have not tried this. All the grain is in the mash, only.
It's a fine recipe and if executed well, will produce a very good pint of Beamish.