The UK negotiated an opt out to the 48 hour maximum enforced by the European Working Time directive, though as you say it's something the individual has to agree to (though that can be just by agreeing to a job that stipulates the opt out in the contract).
I live in the UK and work in IT and have never had a contract that didn't automatically opt me out of it, however my wife is a doctor and they're all covered by it so work a maximum of 48 hours.
Worth noting that it's averaged over time rather than a set maximum for an individual week.
Also worth noting that individual countries can have stricter policies. I believe France has a lower maximum.
Of course there are substantial subsets of UK workers that "can" stick to 48 hour working hours, but where "everyone" know full well their career is fucked if you don't opt out.
Major law firms, for example, where the expected level of billable hours might eek in below an average of 48 hours, but given the amount of non-billable time, it's basically impossible to meet expectations and get promotions if you don't opt out, and you'll eventually find yourself sidetracked so thoroughly there's little reason to stay.
My ex works in one of those places - one of the magic circle law firms -, and she keeps fantasising about opting back in once she's set aside enough money that she can risk having legal career go down in flames.
I live in the UK too, and work in IT, and have never seen a contract that even mentions the working hour directive at all. If I did come across one, I'd probably laugh in their faces and leave, as it'd indicate bad things about the working environment to me.
At the moment I work strictly 9-5 due to childcare commitments (though I do occasionally have to handle emergencies from home). As in, I leave between 5pm and 5.04pm or so, every day.
The contract is fine but a worker can cancel the opt out if they wished (in writing, giving I think 7 days notice) and (in theory at least) they can't be discriminated against for doing so.
Worth noting too that the average of 48 hours a week is calculated over 17 weeks so under even under a WTD compliant agreement you could have someone work a month of 60 hour weeks so long as you reverted to 40 hour weeks for a while after to bring the average back down.
The problem here is that any piece of legislation in this category with a "in theory at least" clause against discrimination will become meaningless. This type of legislation must be mandatory, or at the very least subjected to individual exemptions based on centrally negotiated agreements.
I live in the UK and work in IT and have never had a contract that didn't automatically opt me out of it, however my wife is a doctor and they're all covered by it so work a maximum of 48 hours.
Worth noting that it's averaged over time rather than a set maximum for an individual week.
Also worth noting that individual countries can have stricter policies. I believe France has a lower maximum.