Do you by any chance know that old British TV series "The Professionals"? I understand English pretty well and I even lived in UK for 2.5 years but for some rea

Do you by any chance know that old British TV series "The Professionals"? I understand English pretty well and I even lived in UK for 2.5 years but for some reason this TV show is really difficult to understand for me - half of the time I cannot figure out what they are saying and I do not know why. Is it some local dialect or something?