I doubt very much that the recipe is complicated, or that it contains anything more exotic than their supplier's pale malt, a few percent dark crystal and maybe some brewer's invert sugar. The hopping schedule is likely to just be 60 and 10 minutes. The secret sauce with bitters is the combination of the brewer's water, their yeast and how it all comes together with their equipment.
If you get hold of a copy of (the late) Graham Wheeler's "Brew Your Own British Real Ale" it has dozens of clone bitter recipes in it and they pretty much all follow that same basic formula.
If you get hold of a copy of (the late) Graham Wheeler's "Brew Your Own British Real Ale" it has dozens of clone bitter recipes in it and they pretty much all follow that same basic formula.