Работа в Скотленд-Ярде. Все подробности и нюансы.

только подданные ее величества

Подданство нужно в первую очередь, решите этот вопрос - будет смысл обсуждать дальше, пока что вам до этого как до луны и пока вы его получите правила изменятся миллион раз .

Вы соответствуете всем этим критериям?

Applying to join the police
You'll first need to check that you meet the minimum eligibility requirements. These vary between police forces, but in general you should:
- be aged 18 or over
- be a British citizen, a European Community (EC)/European Economic Area (EEA) citizen, or a foreign national with indefinite leave to remain in the UK without restrictions
- have lived in the UK for the last three years (although there are exemptions, such as if you've served abroad with the British armed forces)
- possess a qualification equivalent to A-level, have been a special constable who has been signed off for independent patrol service in the last two years or have served as a police community support officer (PCSO) for 18 months.

И не забудьте:
You can't apply if you've made an unsuccessful application to a police force in the last six months.

https://www.prospects.ac.uk/jobs-and-work-experience/job-sectors/law-enforcement-and-security/joining-the-police

И 19 килофунтов в год на старт - это явно недостойная zарплата.
https://nationalcareers.service.gov.uk/job-profiles/police-officer

В любой стране для работы в правоохранительных органах нужно гражданство или подданство.