Screwies looks accurate based on what you would assume James Squire do, and based on the fact they list crystal malts only on the bottle or whatever.
But if you want a more simple recipe that's very close, and which I recommend for beginners as I've done it many times in extract, partial and all grain, then do something like the following.
4500g Ale Malt (Barrett Burston)
350g Caramunich II Malt (Weyermann)
40g Chocolate Malt (Bairds)
40g Willamette @ 60 minutes
20g Willamette @ 15 minutes
US05 Yeast
Mash at 66 degrees.
This is for 20 litres at 67% efficiency.
Once again I must say I'm not saying this is a better recipe, just perhaps a better recipe for a beginner as it's single hop, less grains, and no sugar etc.