In 1953, Field was spotted by a policeman acting suspiciously in public lavatories in the West End of London. The officer arrested him for "importuning for immoral purposes", an offence which meant seeking out homosexual partners. Field gave his occupation as biochemist and pleaded guilty, but when the press discovered his real job and reported the case, he changed his plea to not guilty.

Field was convicted on one charge and fined £15. He immediately appealed, with his defence led by the Conservative MP John Maude who was reported to have given his services free. Maude was a spirited advocate for his cause, accusing the policeman involved of having committed perjury. However, Maude could not persuade the Appeal Court and the conviction was upheld.