In Butler's, Picasso met many painters - and decorators and steel workers and bus drivers.
Sheffield was the venue for the second World Peace Congress, a movement suspicious of Western rearmament and sceptical of the Red menace. Picasso addressed the congress and also drew a dove of peace on a Butler's napkin.
The peace congress and the napkin have been lost, metaphors of the post-Soviet age made more potent by the catastrophic loss of business Steve and Edna Butler have endured since the council's traffic managers caught cubism.
The latest in a series of new one- way streets, bus lanes and accommodation for a 20-mile long tramway have increased traffic past Butler's. But bold double yellow lines have stopped Butler's customers parking outside and restricted times of day when huge potato pies can be loaded for outside catering.
Revenue fell by about 20 per cent. 'It is just about to put me out of business,' Mr Butler, whose father fried the cafe's first egg in 1910, said.
'We were going to pass the business on to Andrew, the lad who cooks downstairs and who's been with me since he left school 21 years ago. All the staff have been here all their working lives, but it's just not fair to him if it's not saleable.'
John Lashmar, a city council traffic manager, said the changes represented 'the biggest thing to hit Sheffield since the war - there are teething troubles, but it is working surprisingly well considering how radical it's been'. Mr Butler claimed his complaints had met council inertia, but Mr Lashmar said parking regulations for a side street clogged with cars parked all day will be changed so Butler's diners can find a bay.
Prospects are less sanguine of finding Picasso's 'Dove of Peace on Napkin with Egg Stain', whose existence has become the stuff of fable. The Peace Congress was denounced as a Moscow front. A Conservative MP, Reginald Bevins, demanded it should be banned, the Labour Prime Minister, Clement Attlee, described it as 'bogus', the Government refused entry to two out of three overseas delegates and Labour Party members were forbidden to attend. Sheffield's obstreperous Labour councillors refused to cancel the bookings and congress meetings overflowed.
Old socialists speak of the napkin entrusted to the attic of a safe house, to reappear when the day dawns, an ark of the left covenant. Others say a Communist Party member in Chesterfield had it and he is dead.
Steve Butler has heard more napkin tales than he has served puddings. 'But I've no idea what's happened to it.' Nor have today's Labour councillors, many of whom embrace the new realism. 'I wish we could find it,' one said. 'We could sell it for a small fortune.'