It is a very old English recipe I suspect from the days when dried fruit was to expensive for the ordinary person and probably carroway seeds were plentiful.
May even have been that many people working in service or the like may even have been given these by their employer (or heaven forbid acquired them - probably easier than acquiring dried fruit).
Poppyseeds have never really been that popular in England in recent times though we have dusted them over bread and put in the ocassional loaf but carroway seeds were much more popular. Having said that it is now hard to buy them apart from in very small quantities in top class supermarkets or health food shops. I buy mine by mail order as it is much cheaper.
If you make the cake in a loaf tin you can slice and butter it but I find it rich and moist enough without doing that though I do not cook it as long as the recipe says.
still cold over there?