I've stayed in London many times, and this is my favorite location to form a home base. This past spring I was there for just a night in between international flights, and stayed at the Mornington. Just steps from Hyde Park and the Central Line at Lancaster Gate, it's easy to get anywhere in the city, or just take a walk in the park or to one of the nearby pubs (We like The Mitre. After two weeks in Italy, a beer and chips felt incredible.)
Our double room was fairly tiny, but nothing unexpected by London standards. Consider it an exercise in creativity! You CAN fit yourself and your stuff, you just have to be strategic about it. And we had a nice city view, which helped. The bathroom was actually quite spacious.
The staff were very welcoming, and even loaned us an outlet adaptor, since we'd been in Italy and forgot to pack a UK one just for a night. Hooray for charged phones! There was also a nice little library-style bar, which we did not try, but I'd encourage you to, because they had a nice selection of food and drink at a reasonable price in a nice little corner off the lobby.
Breakfast was ENORMOUS. The coffee suffered, but like I said, we'd come from a two-week stint in Italy, so just about anything was going to be a downgrade. ;) That being said, the overall breakfast selection was bigger than any I've ever seen in London, and the fact that we got it included in our rate was outstanding. We even had a manager come around as we were eating to check and see that we were satisfied, which was nice.
Overall, a lovely hotel with a friendly, accommodating staff and fantastic location -- what more do you want? We'd definitely stay again. less