East Wing Rooms at the Metropole are quite compact and don't really have enough space for a rollaway. Since the East Wing has the Exec rooms it is the default upgrade option. I haven't stayed at the Metropole for over 12 months but in over 20 stays I have never had a non East Wing room, and all room dimensions were the same. The West Wing I understand has bigger rooms but it used to be that a West Wing room was not an Exec room and thus did not come with lounge access by default. This is less of an issue with guaranteed lounge access for Diamonds but I still think they tend to push the East Wing.

I have had a similar number of stays at the Paddington which is much more variable in terms of room dimensions. As an older property the location and floor of the room plays a part in the overall dimensions, true Exec rooms (and it has been rare in my experience to get one) are quite a bit larger than standard rooms. The standard rooms are uniformly larger than the East Wing rooms at the Metropole. Many of the standard rooms would easily accommodate a rollaway bed but in some circumstances it would be a tight squeeze. The best of the Exec room types at the Paddington have a walk in study area, which would make a good space for a rollaway bed and give more privacy than most non suite type rooms.

The Docklands Hilton has the only rooms I have ever seen with beds for 3 as standard in the "family room" category. I don't think any other London property has this layout which avids any potential extra bed charges. The Canary Wharf Hilton has some very large standard rooms (larger than Exec Rooms) which would quite easily accommodate a rollaway bed, an Exec room at this property wouldn't. Similarly the Hilton Tower Bridge would accomodate a rollaway bed in the larger rooms which straddle a corner in the floor plan but not in other types.

It is a shame my old favourite The Conrad at Chelsea Harbour (now a Wyndham) is no longer a Hilton property. This hotel was/is all suite and has a minimum of a King Bed and double sofa bed in every room.

I can't think of any other London Hilton property (and I have stayed at them all several times apart from the Bentley and Courthouse) aside from the Paddington and the Docklands where you could guarantee accommodating 3 people. In some properties you would have no problems in the right room type but whether you would get that room type would be open to question.

I wouldn't choose to stay at the Hilton Docklands as a tourist though.