Some airlines such as Turkish offer a free hotel night with an overnight stopover in Istanbul, regardless of class of service. It’s a little-known benefit that applies even to economy travel and helps Turkish make more sense as a carrier of choice for travel to and from destinations that don’t get a ton of service, where picking Turkish requires spending the night.

Several carriers, especially in the Middle East, will offer a similar service for premium cabin customers at least on paid fares.

But British Airways has come out with a promotion offering London hotel nights, potentially even two free nights, and is offering it with any paid roundtrip ticket to London this summer originating in the U.S. regardless of booking class.

Purchase travel between the U.S. and U.K. through Thursday, July 25 for travel between July 27 and September 30, and one passenger traveling alone gets a single night and two passengers get two hotel nights.

The six participating hotels are Tavistock, Royal National, President, Astons Apartments, Doubletree London Westminster, and Rembrandt. They dub the Tavistock a “2.5 star” and the Doubletree and Rembrandt “4 star,” the other three as “3 star.”

Here are the terms and conditions.

After choosing your flights at BA.com, select “add to your flight” and choose to add a hotel. Enter your dates, select one of the free hotels, and it will be included in your booking.

If you want more nights at the given property besides the free ones, you need to create a flight and hotel booking under ‘create a trip.’ Then you can include up to two free nights as part of a longer hotel stay.

I haven’t tested if this works with London as a stopover destination and not the final destination in a multi-city itinerary, but it wouldn’t appear to under the terms and conditions of the offer.

British Airways codeshares on joint-venture partners Iberia and American Airlines are eligible.

There are a few tricky rules here and there:

• Royal National, Tavistock and President hotels require a 3 night minimum stay between July 27 and August 13 which means you must come out of pocket at least one hotel night (for two passengers on the booking, for a solo passenger it would be coming out of pocket two nights, so choose a different hotel).

• Four of the six hotels include breakfast, the Doubletree and Astons Apartments do not.

• Only the Royal National Hotel will allow 3-4 people in the room.