From 1 Feb to 30 April 2017, you can earn up to Quadruple Avios with stays at Hilton Hotels.
Hilton typically just need you to register and the bonus then applies to already booked reservations normally. Most of my booked stays are pre-paid so I may not earn the bonus Avios if the website booking is real.
Double Avios is applicable for stays booked and completed at the Participating Properties on any second stay during the promotional period. Triple Avios is applicable a third stay booked and completed with within the promotional period, and quadruple Avios is applicable on any fourth and more stays during the promotional period. A stay is defined as consecutive nights spent at the same Participating Property, i.e. from check-in to check-out irrespective of the length of stay. You need to have your account set to Points+Miles in order to earn airline miles as well as points.
There is no link to the list of participating properties, but I will keep an eye out to see if that appears soon. The web site wasn’t even working first thing this morning, although it came to me in a BA email overnight.