Truthfully? I'd remove the curtain that's falling off the track completely if it can't be fixed, and I'd get professional carpet cleaners in (if you haven't already from the end of tenancy). Otherwise I wouldn't change anything. If you paint it, is it really going to make much of a difference? It's all neutral at the moment. If, on closer inspection, the paint is really scuffed, you could repaint, but your problem isn't people walking away when they view, it's getting them through the door.
The kitchen isn't as up to date as many people would like nowadays, but no matter what you spent or put in, you can't please everyone. It's functional and new enough to not need replacing imminently.
It's a nice house with 3 decent sized bedrooms. OK, so the en suite is a little small, so what (I do agree to maybe put a cool white/daylight bulb in there rather than the warm/yellow white).
Your biggest issue is the market. London is still bouyant, but other parts of the country have just stalled. There are other properties in the area that have been on the market since October/November/December.
Also, it could just come down to price. There's a larger 4 bed detached online (sold) listed at £485k and the one listed in November is a 4 bed for £495k.
The closest 3 bed in price is £450k, which is more modernised.
I agree with what others are saying about the photos (yours look like the estate agent's taken them with an old iphone 7 or something!) and floorplan. This property from the same agent has much better pictures and floorplan. I'd get them back to retake them and redo the floorplan to something that doesn't look like it's been put together by a 10 year old using Paint.