American English to British English: Letter J

Jack (cards) Knave (cards)
Jack Socket
Jail Gaol
Janitor Caretaker
Jell-O TM Jelly
Jelly Jam
Jelly roll Swiss roll/jam roll
Jeopardize Jeopardise
Jeweler Jeweller
Jewelry Jewellery

Jibe Gybe
John Doe Joe Bloggs
Jr. Jnr.
Judgment Judgement
Judgmental Judgemental
Jump rope Skipping rope
Jumper cables Jump leads
Junior Undergraduate (3rd year ~)