Edited by GeorgeSR - 6/8/16 at 10:51pm
£200 suit for interview
The fit is pretty admirable for off the rack. I'm no professional, but if you told me it was MTM I would probably believe you.
As far as one button suits go, there's a really good chance that nobody will even notice. Yes, one button suits are pretty casual, and in a conservative office setting they may not fly, but I wouldn't exactly worry too much about what you have there. We don't close the bottom button on suits anyway.
Sleeves are definitely too long, think it needs to be at least an inch shorter. Wear one of the shirts that you'll typically wear to work and get a tailor to do the exact measurements.
Length looks fine to me for a one-button. It's not as serious a color as the typical business suits and you're a young chap who's in decent shape, don't worry about the length.