just a normal British bit of vernacular, bordering on slang.So contrived he tripped over it..
Wiki tells you the details:
- The long version Bob's your uncle and Fanny's your aunt meaning "and there you are" or "it's that easy!" or "(after that) it's done!" or "(after that,) you have achieved what you wanted to achieve". One variant is Bob's your uncle and Fanny's your granny. Other variants, of both versions, spell your as yer.
- This longer version may have been shortened to Bob's your uncle because Fanny has taken on a sexual meaning (late 20th century) since the expression was coined (1887).