I had a look over on Jim's homebrew forum in the UK and found this.Not sure of source or accuracy but I suspect it is from one of the books floating around on UK beers.
Obviously gives you a fair scope on the Crystal but I think using something like CaraRed or Caraaroma would go well. Or you could mix it up between those and some dark crystal.
St. Peters Ruby Red Ale
St. Peters Brewery - Bungay, Suffolk, UK
Category: Bitter
ABV: 4.3%
IBU: ≈22
Grainbill: 92.5% Pale, 5% Crystal Malt, 2.5% Chocolate Malt
Bittering Hops: Challenger (90 min)
Aroma Hops: Styrian/Savinjski Goldings, Cascade