In my experience (non EU, non UK citizen) I have only been asked for the passport during check-in, as this is my legitimate ID when I am traveling.
During reservation, I have only been asked for a credit card number (and billing address).
I would find it very odd to be asked for my passport information at the time of reservation.
In many parts of the world, hotels are required to keep this data on file, mostly for security purposes but increasingly for taxes and other data aggregation. In these scenarios the information used is anonymized – as it is only valuable in aggregate.
In some countries, they are required to keep the non-sanitized information for a certain number of days beyond the end of the reservation as required by the immigration authorities.
Source: consulted on such a project for a large multinational hotel operator.
I am not a hotel operator, but something similar, an Airbnb host. Here is my experience with the local law. I am obligated to provide the guest’s passport number, nationality and home address when I file my tax report.
It is really damaging to me because privacy-conscious persons prefer to do things the illegal way, with a hotel or operator who doesn’t care to take these data (usually because they evade taxes by not filing these reports).
Some hotels in the UK […] nevertheless ask would-be guests to supply their passport numbers in order to confirm their bookings
What recourse does a person have in the case where a hotel in the EU asks for a passport number in order to confirm a booking?
You can go to another hotel. Source: I spend about 30 nights per year in UK hotels, and never bring my passport. The only ID I provide in a UK hotel is my credit card.
Other EU states might have more stringent requirements in line with local laws.
In some states, hotels are legally required to record the passport or ID card number of all guests. Asking during the reservation and not after arrival is not much more intrusive, unless the computer you’re working from is compromised.
Edit: I don’t have an exhaustive list, but here is one example (scroll down to section 21 a).
Credit:stackoverflow.com‘