The trauma of the Government's defeat over Sunday trading in 1986 has an honoured place in the folk memory of Cabinet ministers. It was, after all, the only defeat in the Commons for a piece of primary legislation in the 12 years that Margaret Thatcher was in power.
Which is the main reason for John Major's more cautious approach. Even though he and Michael Howard, the Home Secretary and the direct sponsor of the Sunday Trading Bill published on Friday, are in favour of total deregulation, they have been careful to provide MPs with a series of options - now narrowed down to three - and allowed them a free vote.
Total defeat would be a humiliation, leaving the law in its present confused and messy state. But that is now widely seen as unlikely.
Also unlikely is the total deregulation privately favoured by most of the Cabinet. The big parliamentary battleground is between the supporters of two options. One is based on the uneasy compromise between Marks& Spencer and the Keep Sunday Special campaign, which would restrict the big stores to opening for the four Sundays preceding Christmas, and the other is favoured by the Shopping Hours Reform Council which would allow big stores to open for six hours every Sunday and small ones all day.
Supporters of both predict that the vote will be close, though events in the past few weeks have strengthened the SHRC camp. The first is that Usdaw, the shopworkers' union, which fought a highly successful campaign against deregulation in 1986, has, under pressure from many of its supermarket members, switched its line to support for the SHRC option.
The second is the U-turn announced by the Government yesterday which will give workers the right to refuse to work on Sundays. Finally, the concession to pre-Christmas opening by the Keep Sunday Special campaign has undermined its moral argument against Sunday shopping.
The best bet is that the SHRC option will carry the day. The Bill has been introduced quickly so the law can be clarified before Christmas. But it is close; there are many days of wheeler-dealing and lobbying ahead.