The secular society in France does not mean that Christmas, Easter etc are not celebrated, in fact we have more religious bank holidays than the UK. In May there is not a single week without at least one saints day in it.
All it means, is that religion cannot have any political power or state funding, so there are no state funded faith schools and all public offices cannot have any religious symbols on show. A town hall here has just been fined for having a nativity scene on it's frontage so it is strictly enforced.
However most French people are regular church goers and Sunday opening has never really been embraced even though there is nothing to prevent it. I think that is more because they see Sunday as a church and family day and want to keep it that way.
What to buy for 18th birthdays?
Another Tired Kicking For The Sick And Disabled By Rishi
To think that London, or anywhere else for that matter, does not belong to any one demographic