I Love a Lassie 

They received the Scotch peer with huge delight. He reminded them Harry Lauder and they said so. [...] They implored him to be a pal and sing 'The Saftest of the Family'. Or, failing that, 'I love a lassie'.

Psmith in the City. 10 Mr Bickersdyke addresses his constituent

He thought for a moment; then threw his head back, shut his eyes, and let it go in a musical baritone.

'I love a lassie, a bonny, bonny lassie,' sang George. 'She's as pure as the lily in the dell.'

'No doubt,' said the specialist, wincing a little.

'She's as sweet as the heather, the bonny purple heather – Susan, my Worcestershire bluebell.' 

Meet Mr Mulliner. 1 The Truth about George

There was a stage wait of about a minute and half, during which, my moodiness now much lightened, I rendered 'Roll Out the Barrel', 'I Love a Lassie', and 'Every Day I Bring Thee Violets', in the order named.

Jeeves and the Feudal Spirit. Chapter 1