It is a sturdy, symmetrically built, working terrier like an old-fashioned Ilmer Sealyham type, created only by crossing an existing Lucas Terrier with a Norfolk Terrier or with a small Sealyham Terrier. A latter-day Norfolk Terrier mated with a latter-day Sealyham Terrier does not produce a Lucas Terrier because it will not trace back to the original Lucas Terrier lines. All true Lucas Terriers have a direct connection to Sir Jocelyn Lucas’s original Ilmer Kennel based Lucas Terriers. The Lucas Terrier is bred primarily for temperament and companionship, and so should be friendly, with no aggressive tendencies towards people or other dogs, and not fearful or nervous while retaining the usual terrier traits. The coat should be fairly harsh, weather resistant and of medium length. It may be coloured or white, but the majority are tan, black and tan or saddle and tan. Dogs should weigh 14–20 lbs (6–9 kg) and bitches 11–17 lbs (5–8 kg).