becky, we stayed at the Celtic two summers ago.. and have booked to stay there this May.
We loved the hotel. The breakfasts are great, several courses, all cheerfully served ( with many choices, just ask)..
The staff are friendly.
The room we took was a double with bathroom ensuite, and had a fireplace in it ( not functioning anymore but so atmospheric )..
Bed was comfy.
Bathroom was small but completely functional.
We were only one flight up , and as I recall there are only a few floors anyways.
It was very convenient pleasant area.. just 1/2 block down from St Russell Square. We had an easy trip back to airport from there too( station was a block and half away) .
Obviously since we have rebooked we liked it.
We also stayed in another spot ( we had booked 4 nights at beginning of our trip in London, and 4 nights at end, we stayed in Celtic on last four nights) and it was about the same price. It was horrible. Bathroom so small you could barely bend over sink to wash face, and when we ran out of toilet paper , the maid in the hall way handing me HALF a roll and said that's all she had .. seriously. No breakfast included. And bed was shoved in corner of room with only a foot between wall and bed on the "open" side. So,, for the money we were thrilled with the Celtic after that fiasco.
Its "homey".. you really feel like you are in a small family run British hotel ( which you are !) , its not fancy.. but clean and good location, and for the price unbeatable.. London is super expensive to us ( and now with our Canadian dollar tanking this is even more of a point,)
Only caveat.. no airconditioning, which usually is not an issue in London.. but we had one warm day and asked for a fan. That worked.