We booked a hotel room 3 days before arriving in London and got a confirmation from Elvoline.
After 1d we got informed that Elvoline wasn't able to get a room from the hotel we chose and offered another one (double the distance from sights we wanted to visit and with lower ratings).
We called and asked for a different offer. One day after that we were offered a hotel, comparable to the one we originally booked. We agreed to take this offer.
On the day of our flight we received an email, telling us that Elvoline (again) had not been able to get the room confirmed by the hotel and we would get our money back.
Therefore, 3 days after booking a room through Elvoline, we ended up not having a reservation at the day of our flight to London.