The obsolete British-English phrase a handsome husband and a thousand, or ten thousand, a year (in which pounds is omitted after thousand) denoted the ideal of an unmarried woman.

The text containing the earliest occurrence that I have found explains the signification of this phrase: the following paragraph was published in several British newspapers in May and June 1907—for example in The Motherwell Times and General Advertiser (Motherwell, Lanarkshire, Scotland) of Friday 17^th May:

From this week’s “London Opinion.”
[…]
A handsome husband and ten thousand a year was, in the old days, supposed to be the summit of a girl’s worldly ambition. Nowadays we have changed all this. The handsome husband who used to be the beau ideal of the maiden’s fancy must be replaced by a foolish one, who allows his wife unlimited freedom, and exempts her from all responsibility; while the ten thousand a year is the very lowest figure to be aimed at by the average marriageable maiden, who thoroughly understands that love in a cottage is anything but ideal.

The phrase also occurs, for example, in the following from the Birmingham Gazette (Birmingham, Warwickshire, England) of Tuesday 1^st April 1930:

“Motherhood is the only justification for sex.” This was an expression of opinion last night by the Archbishop of Birmingham quoted at a meeting of the Union of Catholic Mothers, at the Town Hall, Birmingham.
“Why are women more pious than men?” was one of the peculiar questions asked him, said Dr. Edward Grimley. “If women were more pious than men, as the world suggested, it was probably due to the fact that the Catholic religion had done a great deal for women.”
The Catholic Church had always taught chastity and modesty, and that teaching appealed to the sex that stood to lose most when those ideals perished. They upheld the dignity of marriage and a higher ideal of both sexes, namely chastity.
Some people seemed to think that the ideal of women was marriage. When he was young he was once asked: “What is the maiden’s prayer,” and was told it was for “a handsome husband and a thousand a year.”

The phrase was especially used when offering to an unmarried woman the last cake or piece of bread from a plate—as in the following passage from Choosing a Bride, an unsigned short story published in the Evening Telegraph and Post (Dundee, Angus, Scotland) of Tuesday 8^th November 1910 (Betty Willoughby is in love with “handsome young Harley Dering”, who is about to work abroad and is in love with “beautiful Vera Maitland”):

“Oh, Harley, this is nearly the last of our jolly excursions,” sighed Betty Willoughby, looking at the young man opposite with suddenly clouded eyes.
“Yes,” agreed her companion. […] “Ten thousand a year and a handsome husband,” added Dering, handing her the plate containing a solitary cake. “No? Well, I suppose we must get home again.”

The following, from the Aberdeen Daily Journal (Aberdeen, Aberdeenshire, Scotland) of Tuesday 28^th February 1922, explains why the phrase was used when a single cake or piece of bread was left over on a plate:

PRE-WEDDING BELIEFS.

There is a cloud of pre-wedding beliefs, from our own “handsome husband (wife) and a thousand a year” (the lot of the one who takes the last cake or piece of bread from the plate) to the strange supper-table custom of the Serbian girl who wants to know what the future holds in store for her. She lays on one side the first and last crumbs of the bread, fastens them together with a piece of wood, and puts the whole affair under her pillow. It is suggested that her destined husband will then appear in a dream at midnight.

The British custom is jocularly evoked in From Cocktails to Port, by ‘the Shaker’, published in The Illustrated Sporting and Dramatic News (London, England) of Saturday 11^th April 1925—wife is substituted for husband, or for and, and the annual income is five thousand:

Little Jock Macpherson was attending his first children’s tea-party, at which he did great execution. “Now then, Jock,” said the hostess with a smile as she offered him the last cake, “Here’s a handsome wife or five thousand a year.” “Yes,” said little Jock cautiously, “but is the five thousand nett or does income-tax have to be deducted?”

‘M. U. S.’ mentioned the custom in Riches and Poverty: A Matter of Degree, published in The Manchester Guardian (Manchester, Lancashire, England) of Tuesday 11^th February 1930:

When the last piece of bread-and-butter came round on the plate we used to press it upon one of the bachelor girls. “Come on, now. It means a handsome husband and a thousand a year.” The thousand a year certainly sounded an alluring part of the bargain.

This British custom was compared to a French one in Women’s Sphere, published in The Halifax Courier and Guardian (Halifax, Yorkshire, England) of Saturday 29^th July 1939:

Wine is very cheap in France, and in consequence is much more widely known. Most families drink wine with their meals as a matter of course. Therefore, it is not at all surprising that our superstition when handing the last piece of bread or cake from a plate should have an equivalent superstition over there in the last drop of wine from a bottle. We say, “A handsome husband and thousand a year,” when passing the last piece; they offer the last drop of wine to the unmarried girls and say, “A husband for you before the end of the year.”