Walden, Crafter, Seagull (s6 folk/other variants) Yamaha G series, all pretty much under £300-400 and will sound great.
I have a seagull s6 folk and it's a lovely guitar - lots of midrange bark due to the slightly smaller body, it's a very loud guitar for its size, better than comparable dreadnoughts I've played.
Mate of mine has a Yamaha G series and it plays very well for a guitar under 300 (I think he paid 260 for it?) it's nice and bright, with good tone and sustain on the harmonics etc.
Walden make some nice instruments by the looks of it,
http://www.waldenguitars.com/G630CE.html seems to average ~ £340 for a semi acoustic with a cutaway. This looks like a nice guitar to me - obviously it depends on what it sounds like, but if you're looking at a semi acoustic, play it unplugged and make sure you also hear it through an amp; a guitar that doesn't have much 'voice' or 'presence' unplugged but has a good tone will carry that tone when amplified so don't worry about acoustic volume with a semi acoustic guitar. Ask the guys in the shop about amp setups for a good tone setting etc.
I think your budget of 300 (if you can stretch to 400?) is just right for something you can learn on and give some stick. If you do decide on a guitar, haggle with the shop for a hard case as part of a deal (why I suggest up to 400). Nothing worse than dropping your guitar and it breaking.
Things to look for - string height.... low as possible without fretbuzz. Straight neck with no hump where the neck meets the guitar body (usually somewhere after the 12th fret - look for this if you decide to buy second hand, it is an indicator of a dry guitar where the join between the neck and the body of the guitar has contracted. Not much you can do to correct this except a re-fret or more expensive yet, a neck reset). Good harmonic sustain in on all of the dots (you know what I mean?).
C'mon man, get out there and play some guitars and let us know what you're looking at and how they felt!
)
