Here are the actual requirements from the DOS manual -- https://fam.state.gov/fam/09FAM/09FAM050207.html#M502_7_3_C_3
"If the applicant is 16 years of age or older, they must obtain an original or certified copy of a police certificate, if obtainable, for:
(a) (U) Their country of nationality, if they lived in the country of nationality for more than six months at any time in their life;
(b) (U) Their current country of residence, if different from nationality, if they have lived in that country for more than six months; or
(c) (U) Their previous country or countries of residence if they were 16 years or older at the time they lived there and lived in that country for 12 months or more; and
(d) (U) Any city and/or country where they were arrested for any reason, regardless of how long they lived in that city or country and regardless of age at the time of arrest.
(e) (U) See U.S. Visa Reciprocity and Civil Documents by Country for availability of police certificates for individual countries.
(f) (U) Present and former residents of the United States do not need to submit any U.S. police certificates."
Based on item (a) above, seems to me you'll need police certificates from the 1st and 2nd countries because you lived there for more than 6 months, assuming you have citizenship in both countries. The policy doesn't say you need PC only from the country of current nationality. But obviously, you'll need a PC from the UK as well.