The date 1352 is inscribed over the low doorway.
1910: Barley Mow in Thames Valley Villages by Charles G Harper

The Barley Mow at Clifton Hampden
The Barley Mow at Clifton Hampden.

Sheila Llewellyn, The View from the Bridge -

The original Barley Mow was half timbered, of cruck construction, with a thatched roof, made of wych-elm supported by eight vast timbers. The oak panelling inside is at least 400 years old.

1873: Advertisement -

Advert for Barley Mow at Clifton Hampden
1873 Advertisement

1877: The Barley Mow, Henry Taunt -

The Barley Mow, Henry Taunt, 1877
The Barley Mow, Henry Taunt, 1877 (Timbers white-washed)
© Oxfordshire County Council Photographic Archive; HT2048

1884: The Upper Thames, Harpers New Monthly Magazine -

We know that ... there is for the end of our journey pleasant quarters at the Barley Mow.
It was Sunday evening when we took up our quarters for the night at this quaint little tavern, with its thatched roof and clean sanded floor.
The villagers had been to church. Some of them were walking homeward, prayer-books in hands; others were assembled on the benches outside the inn, engaged in local gossip and cracking rustic jokes. The scene had a pastoral look, with which the old gabled cottage and the broad gentle river were in poetic harmony.
The weather on the morrow, and its suitability for fishing, and a recent boatrace, appeared to be the chief topics of conversation; but as we strolled through the village some of the good folk were discussing the sermon in a friendly kind of way.
It is a village outside the world, linked only with distant cities by the silent river - a village where, in comparison with life in London, a day might seem a month.

1885: Dickens's Dictionary of the Thames -

On the Berkshire side, two or three minutes walk from the bridge is the "Barley Mow", one of the thatched, sile built, old-fashioned resting-places which have been almost improved out of existence by the modern system of hotels. The parlour of the "Barley Mow" is a queer panelled room, more like the cabin of a ship than the coffee-room of an inn, and is of so low a pitch as to still further favour the illusion. But although the house is primitive, and the entertainment unpretending, it is a capital little inn of its class, and may be recommended to boating men.

1885: The Royal River

One of the most charming 'bits' at Clifton has neither been sketched often nor described quite so often as it deserves to have been.
The Barley Mow is assuredly the oddest and quaintest of inns on the river.  It lies on the Berkshire bank, in a little roadside corner all to itself.  What its age may be it would be difficult to tell; but its high, overhanging roof is thatched and its walls are half-timbered.  The diminutive casements, about the size of the door of a rabbit-hutch, admit just enough of light to heighten the interior effect.  Broad masses of light are out of place within such venerable walls. 
The brick-floored kitchen - or maybe it is the parlour - is delightfully snug; the walls panelled darkly all round; the honest raftered ceiling is so low as to do away with the necessity ever to stand upon the naked wooden settles to reach things; the fireplace extending across one whole side of the room, the oddest imaginable cross between an old-fashioned ingle-nook open grate and a modern kitchen range; the chimney piece garnished with many a brightly-burnished pot and pan.
No demure Phyllis makes her appearance; but the cider – we are in a great cider country – is nectar.
At the back of the inn is just such a queer little garden as Dickens loved to write about.  All the flowers were our great-grandmothers', and indeed modern daintinesses would sadly mar the antiquated aspect of this typical roadside inn of a day that is long past.

1889:  Jerome K Jerome -

Round Clifton Hampden, itself a wonderfully pretty village, old-fashioned, peaceful, and dainty with flowers, the river scenery is rich and beautiful.
If you stay the night on land at Clifton, you cannot do better than put up at the "Barley Mow."  It is, without exception, I should say, the quaintest, most old-world inn up the river.  It stands on the right of the bridge, quite away from the village.  Its low-pitched gables and thatched roof and latticed windows give it quite a story-book appearance, while inside it is even still more once-upon-a-timeyfied.

1890: The Barley Mow at Clifton Hampden, Francis Frith -

1890:  The Barley Mow at Clifton Hampden, Francis Frith
1890:  The Barley Mow at Clifton Hampden, Francis Frith

1891: Elizabeth & Joseph Pennell, "The Stream of Pleasure" -

The Barley Mow, Thames, Stream of Pleasure, Joseph & E Pennell 1891
The Barley Mow drawn by Joseph Pennell 1891

THERE was no sleeping in the boat that night, for we had appointed a friend or two - the Publisher and the Parson - to meet us at the thatched house, known as the "Barley Mow", which stands on the high road on the other side of the river from Clif- ton Hampden.
River men often make it their resting- place and taste a cup of ale there, for which liquor, as well as for substantial lunches and teas and dinners, and queer little bedrooms hidden away under the thatch, the house is very remarkable.
For this there is the testimony of many in the Visitors' Book, among others of the Lazy Minstrel, and if he be not an authority on the Thames, then no man is.
The hostess is always, with talk running fast as the river, waiting upon hungry people, in the little parlour, where one window looks out on the high road, and the other on the garden, in August full of tall poppies run to seed, and the walls are panelled, and the ceiling is so low every new-comer knocks his head against its huge beam.
We got to Clifton Hampden on Friday evening; all day long on Saturday there was a constant going and coming.
We never went out on the road between the inn and the river that we did not meet a stream of men in flannels and bright blazers; women in blue serges, gay blouses and sailor hats, on their way to the "Barley Mow".

1901: The Barley Mow, Henry Taunt -

Barley Mow, Henry Taunt, 1901
Barley Mow, Henry Taunt, 1901 (framing blackened)
© Oxfordshire County Council Photographic Archive; HT8601

The Barley Mow is still there and still thatched and still quaint - as long as you choose to ignore the arcade machine with its flashing lights and see the candles instead.  And they do still remember where the ferryman sat in the ingle-nook before the bridge was built, which was, after all, only 136 years before I was told about it.
Jerome makes a mistake here (I think).  Coming upstream, one day ends -

... and pulled up to Culham, and slept under the canvas, in the backwater there.

However the following day starts with -

We had finished breakfast, and were through Clifton Lock by half-past eight. 

It is maybe the similarity of the weirs, weir streams and lock cuts at Long Wittenham and then Sutton, that has confused him, as it does me from time to time.

1975: The Barley Mow was gutted by fire -

Barley Mow, gutted by fire, 1975
Barley Mow, gutted by fire, 1975
© Oxfordshire County Council Photographic Archive; D206786a

1977: The Barley Mow was totally restored at a cost of £80,000.
1997: The Barley Mow was rebuilt and rethatched.