I just looked at the listing of the similar property for sale at £10k more. While it's a bit much in terms of decor, it appears a lot bigger than yours, and the interior dimensions are identical! Take the photos yourself if your agent is a bit shit. Make sure the smaller bedrooms are pictured, and shown to be workable bedrooms, because it's hard to gauge from their descriptions alone. Floor plan would help with this too. Also get a picture of your dining area, looking like somewhere you'd actually want to sit down for food, or for a coffee with a friend. Don't stage it with OTT place settings and the like (so naff), but a tidy dining area with the table NOT shoved back to the wall like it's just an obstruction, maybe a bowl of fruit on there, or the salt and pepper mills accidentally left there from last night's tea.
You've definitely over-tidied! Add some personality back in. Not clutter exactly, but as PP said, tea and sugar jars, nice bottles in the bathroom, a picture or two here and there. I'd soften up the sitting room a bit: rug on the floor, those wooden boxes at the end as side tables, picture above the sofa. Top marks to you for not pointing the furniture at the TV. Bottom marks to the agent for pointing the f*%$ing photo at the TV. Make a feature of the patio doors at the other end instead!
The garden is a bit of a let down to me, though I know some people do value low maintenance over a bit of greenery. I understand why people are suggesting a few pots, but I think you need some density of vegetation to make it worth doing, and how many of us can actually afford to do that all at once? I would concentrate your efforts onto the sunniest corner of the garden. Beg, borrow or steal a "nice" garden furniture set (not expensive, but not grotty, scratched white or green plastic!), and get some decent-sized planters and plants for impact. Check your local Lidl to see if they've got any of their potted fruit trees hanging around, or you can often pick up lavender and rosemary plants at local green grocers at this time of year. If you can make the area by the patio doors look pretty, it'll also make the sitting room look better.