We just got back from the Conrad St. James. We absolutely LOVED it! I was a bit nervous about the location and the hotel, but when I walked in and saw how nice it was, I was really happy. From the time we checked in, to the room (so nice!). We had the breakfast every morning, as I added it on to my room. The breakfast was great and the service in the restaurant was beyond great! The manager and the staff were always on top of either refreshing your drinks and refilling the buffet. They also have a menu you can order from and it is included in your breakfast.
Our room was spacious, clean and new. The room has a desk, with closet space, a safe to lock valuables, a beautiful bathroom with a shower and a tub and a separate room for the toilet.
If you need something for the room, you just call them and they bring whatever you need right away. When we needed to go somewhere, the staff would assist. The best part is the tube station is right in front of the hotel, so if you're using the tube, literally its right there.
Westminster Abbey, Big Ben, Parliament are a 2 minute walk a block a way.
I can't say more about the hotel, other than it was great!