Cockney rhyming slang -- a butcher's hook, rhymes with look. The slang gets trickey in use as it is usually truncated. Apples and pears becomes apples, but refers to stairs.
Extremely happy, because one's goals have been attained, one's dreams have been fulfilled and because presenthappiness is expected to linger on and on...
He married his teenage love. He's happy as a dog in a butcher's shop.