You might find a really good rate for a not-quite-central Premier Inn in London for that time period, especially if you are willing to take advantage of the non-refundable option. The savings vary by location and how far in advance you're booking, but I think you might get a 30% discount with a non-refundable reservation. I'm sure you know the Hubs are the low end of their corporate offerings.
If you're not claustrophobic, check to see whether there are any Point As in London.
If you value a hearty breakfast (apparently not skippable to save money), you might check Vincent House, which is one long block north of the Notting Hill Gate tube station. I've used it twice when my visit was in September and I figured being without air conditioning wasn't very risky. It's primarily student lodging, but when I've been there the residents have mostly been over college age, so I'm not sure what the market is. Also don't know how much space they'd have for tourists in February. En suite baths. I believe the beds are all small; that's not an issue for me so it's not something I necessarily remember. I believe you have to email to check on availability, but there is a website for information. I think some of the other student lodgings in London may be less expensive (check London School of Economics), but I'm not sure all rooms have en suite baths.