The British-English phrase if wet, in the vicarage was originally used as a precautionary stipulation in a public notice announcing a forthcoming event such as a church fête, a charitable sale or a presentation.
The earliest occurrence that I have found is from The Thanet Advertiser (Ramsgate, Kent, England) of Saturday 2nd September 1916:
Presentation to Rev. C. C. Cooper.—On Monday a purse of gold, which has been provided by the members of the congregations of St. Peter’s and St. Andrew’s Churches, will be presented to the Rev. C. P. Cowland Cooper, who is leaving the district. If fine, it is intended that the presentation shall take place in the Vicarage garden at seven o’clock in the evening, and if wet in the Vicarage.
The second-earliest occurrence of if wet, in the vicarage that I have found is from the following announcement, published in the Cambridge Daily News (Cambridge, Cambridgeshire, England) of Wednesday 7th July 1920:
ALL SAINTS’, CAMBRIDGE.
SALE OF WORK
THURSDAY, JULY 8th,
3 to 9.30 p.m., in
ALL SAINTS’ VICARAGE GARDEN,
To be Opened at 3 p.m. by
THE MASTER OF JESUS COLLEGE
and MRS. GRAY.
(If wet, in the VICARAGE.)
ENTRANCE 6d.; Children Half-price after 5 p.m.
Proceeds in aid of the Parish Room Fund.
It was sometimes decided to hold the event outdoors whatever the weather—as specified in this announcement, published in The Walsall Advertiser (Walsall, Staffordshire, England) of Saturday 17th July 1909:
A SALE OF WORK AND GARDEN FETE
will be held (wet or fine) in
THE VICARAGE GROUNDS,
On Thursday 22nd July,
To be opened by Mrs. R. A. Cooper
at 3 p.m.
The phrase if wet, in the vicarage refers to the changeability of British weather, as is clear in the following extract from the radio programmes published in the Ealing Gazette (London, England) of Friday 8th August 1980, which, incidentally, contains the earliest figurative use of the phrase that I have found:
Compelling listening on 4 [= BBC Radio 4] at 7.20 pm; Stephen Beard investigates the fickleness of British weather, and the fallibility of its forecasters in If Wet, in the Vicarage.
The phrase has come to be used humorously when arranging, announcing, or speaking of, any forthcoming event—as in the first paragraph of Never mind the size, feel the force of history, by the cricket correspondent and former cricketer Mike Selvey (born 1948), published in The Guardian (London and Manchester, England) of Saturday 30th June 2001:
Next Wednesday morning at half-past ten on the Edgbaston outfield (or if wet in the vicarage) Steve Waugh1 will be presented with the new ICC2 Test Championship Trophy, a “distinctive mace design” from Asprey and Garrard3, all 30 grand’s worth of it, says the blurb.
1 Steve Waugh (born 1965) is a former Australian cricketer.
2 ICC is the abbreviation of International Cricket Council.
3 Asprey & Garrard Limited, London, were designers, manufacturers and retailers of luxury goods such as jewellery and silverware.
In The Guardian (London and Manchester, England) of Wednesday 3rd February 1988, Mike Selvey had already used if wet, in the vicarage in the account of a cricket match between Australia and England, which was played in Sydney and ended in a draw. Here, Mike Selvey likens the error on the scoreboard to the use of if wet, in the vicarage on the posters announcing a forthcoming fête:
Still, drawn the match may have been, but it is a poor fete that does not carry “If wet, in the vicarage” on the posters, and the Aussie vicarage has been the Living Legends’ computer test. At tea-time the final scoreboard was flashed on to the giant television screen above the Hill and it showed, surprise, surprise, that England had failed by 38 runs to score the 287 they needed to win.
The damage was done by the great old leg-spinner, Bill O’Reilly4, who took six for 96, and it would be nice to think that even computers are sentimental because yesterday the Tiger — who since his playing days has spun words instead for the Sydney Morning Herald, often controversial, but always readable — retired from the press box.
His success, I fancy, tickled him a little. “Technology gone mad,” was his passing growl.
4 William Joseph O’Reilly (1905-1992), nicknamed the Tiger, was an Australian cricketer.