The colloquial British-English phrase spit and sawdust means, of a public-house, very basic and lacking in comforts.

This phrase refers to the former practice of covering the floor of a public-house with sawdust into which customers spat—these are two texts mentioning this practice:

1-: From The Everlasting Mercy (London: Sidgwick & Jackson, Ltd., 1911), by the English poet John Masefield (1878-1967)—this poem tells the story of Saul Kane, drunkard and poacher, his spiritual revolt and final conversion:

She took my tumbler from the bar
Beside where all the matches are
And poured it out upon the floor dust,
Among the fag-ends, spit and saw-dust.

2-: From Engineering Notes, by ‘an Expert’, published in the Western Mail (Cardiff, Glamorgan, Wales) of Friday 19^th May 1916:

Catalough’s Foundry […] was taken over by Messrs. Parfitt and Jenkins in 1857, and here the first Cardiff marine engines were made. […]
When these engines were being built much interest was taken in the subject of oscillating engines, which was much discussed by the knowing ones of those days, who, whilst the dignified councillors of the corporation settled the affairs of the town in the cosy little bar parlour of the more aristocratic Angel, were content with the more homely surroundings of the Royal Oak, a tiny hostelry at the lower end of St. Mary-street. A narrow causeway, or side walk, with a couple of steps, led into the street entrance, and on the left-hand side was a small room, with a sawdust-covered floor, and here the engineering questions of the day were thrashed out. On one occasion the subject of oscillating engines was under discussion, and there happened to be present a fitter’s helper, who was suffered to hear and see the designs drawn on the sawdust-covered floor and the beer spillings on the polished table. He at last ventured to suggest that as the engine had been completed, it was time to get in a mason to knock down the walls, as the doorway was evidently too small to get it away; and he suggested that it should be called a B. S. and S. engine, which, he explained, before his summary ejectment, meant a beer, spit, and sawdust engine. I might mention, incidentally, that this particular class of local engineer was known to the apprentices of Cardiff in 1860 as B. S. and S. engineers.

These are the earliest occurrences of the phrase that I have found, in chronological order:

1-: From the account of a social gathering that had been organised at Newport, Wales, to pay homage “to the head of the famous firm of John Lysaght (Limited), of Newport, Bristol, Wolverhampton, and Scunthorpe”—account published in the Western Mail (Cardiff, Glamorgan, Wales) of Monday 5^th March 1928:

The Chairman then proposed the toast of the evening—“Mr. W. R. Lysaght.” In an eloquent speech he paid a glowing tribute to Mr. Lysaght […].
[…]
Mr. Lysaght knew that an employer’s obligation did not cease at the payment of his workmen’s wages. He was not one of those men who walked on one side of the road while his workmen walked on the other side. With him capital and labour walked arm in arm. (Applause.)
He was with his workmen always, whether in the “spit and sawdust” environment or in a hotel.

2-: From The Manchester Guardian (Manchester, Lancashire, England) of Friday 1^st February 1929:

Manchester’s Varied Clubland.
Manchester has a hundred and seventy licensed clubs within its boundaries and a large number of others unlicensed. Between them they attempt to provide for a variety of human needs. Possibly a large variety, but the unlicensed clubs are sometimes hard to trace, and one does not expect anarchists or thieves to advertise themselves. Among the others the variety is no perhaps so wide as a romantic might desire. There is a certain blood brotherhood between the leather lounge club which exists for comfort and seclusion and the kind of club known to a rude populace as the “spit and sawdust.”

3-: From A Dictionary of Slang and Unconventional English (London: George Routledge, 1937), by the New Zealand-born British lexicographer Eric Honeywood Partridge (1894-1979):

spit and sawdust. A general saloon in a public-house: C.20. Ex the sawdust sprinkled on the floor and the spitting on to the sawdust.

4-: From Standing By . . . One Thing and Another, by D. B. Wyndham Lewis, published in The Bystander (London, England) of Wednesday 21^st September 1938:

Darts have now penetrated into West End cabaret. As an after-dinner spectacle you could probably think of something more dizzying than that of a couple of experts performing with a floodlit dartboard any number of clever tricks, but at least the show indicates how far darts have travelled socially from their spit-and-sawdust origins. Few country houses are without a dartboard nowadays, and for all we know Bond Street is featuring boards of rare woods with gold or silver numerals and jewelled darts for chaps in the Spanish shipping trade to give their girls.

5-: In the following from the Evening Telegraph and Post (Dundee, Angus, Scotland) of Wednesday 21^st August 1940, the phrase is used as the name of one of the parts of the room in which members of the armed forces can eat or relax:

Memories of France—8
“Snow White”—With a Black Moustache
How Nicknames Play Their Part in War
BY A B.E.F. ¹ MAN

[…]
Every room or portion of a billet seemed to get a name of some sort, and it stuck. In our sergeants’ mess I was one of five inhabitants of a room known as the “Monastery,” so called, I know not why, because we slept whenever we had the opportunity.
My title in this room was the “Dormant Haggis.” One of us was the “Lay Member,” our “link with the outer world,” who would rise to hear the wireless news, and return to acquaint us of its contents.
Another room was known as the “Jug and Bottle.” The actual mess room was divided into two parts, the smaller being called the “Spit and Sawdust.”

¹ B.E.F. is the abbreviation of British Expeditionary Force.

6-: The phrase is used figuratively in the following from an article about the British theatrical producer George Edwardes (1855-1915), published in the Manchester Evening News (Manchester, Lancashire, England) of Thursday 10^th June 1943:

He raised entertainment from the spit and sawdust of burlesque to a new standard, and in his way was as much responsible for the building of a new reputation for the English theatre as his classical contemporaries Tree ² and Irving ³ and Alexander ⁴.

² Herbert Beerbohm Tree (1852-1917) was a British actor and theatre manager.
³ Harry Brodribb Irving (1870-1919) was a British actor and actor-manager.
⁴ George Alexander (1858-1918) was a British stage actor, theatrical producer and theatre manager.

7-: From Humour in Hansard, published in the Somerset County Herald and Taunton Courier (Taunton, Somerset, England) of Saturday 3^rd February 1945:

Going on to the Licensing Planing [sic] (Temporary Provisions) Bill, the Solicitor-General says that he very much hopes that a house expected to do eight barrels would have more floor space than others doing five, two, or one barrels all put together. “I like,” he tells the House, “to see drinking going on with plenty of space, good ventilation, and good lighting, and not done in dark corners.” Mr. Kirkwood asks if the right hon. and learned gentleman is not forgetting good beer. The Solicitor-General replies that his hon. friend is quite right, and the other things mentioned would be “very vain and insubstantial if the good beer were absent.” He says that he wanted to bring the matter down to “brass tacks.” Brass tacks and ale? Curious how the most erudite of M.P.’s slip up on the matter of metaphors. The classic example is, of course, that of Sir Boyle Roche, who said in the past: “I smell a rat. I see it floating in the air. But I will nip it in the bud.” Mr. Evelyn Walkden refers to “temporary premises” and wants to know who authorises these “ugly contraptions, which take the place of licensed houses that have been destroyed by bombs. They are truly described by some people in the area as ‘spit and sawdust’ places.”

8-: From “Wolf! Wolf!”: Queer Story, by Guy Chesham, published in Truth (London, England) of Friday 8^th June 1945:

At breakfast his publisher returned “Poison Ivy.” At lunch Elaine returned his ring. At three o’clock his rich Aunt Effie returned to life. Not-so-happy returns for Reggie. He resolved on suicide, after tea. However, he’d lost his razor, the river was choked with cans and cats and they had cut off the gas, so he decided to get drunk instead.
“The Plasterers’ Arms.” All spit and sawdust. Soldiers, men and girls in overalls, boozy old women, all drunk and singing. Reggie holds up the bar. Ought he not to be in one of the classier pubs up town? He has already been thrown out of all the classier pubs up town.