I would pass on the Ananda, if you look at the reviews here and general impressions - the "little" brothers are better - the Sundara and HE400SE from Hifiman. Then there's something like the 560s from Sennheiser which was recently reviewed by Amir. Audio Technica AT-R70X might also be something to look out for - I know some people find them uncomfortable though - and as much as people put stock in measurements here, if a headphone is uncomfortable it ends up collecting dust more often than not.
I have both the Sundara and 560s - happy with both - if I had to recommend one of them it would be hard - the 560s are light, it's Sennheiser so even if they are plastic they will probably outlast most headphones, but from user experience there seems to be quite a bit unit to unit variation in quality control - but, they can be had from Amazon or Senn themselves or any number of reputable sellers in the UK and easily returned, even multiple times until you get a good quality pair (mine were fine out of the box and have been). The Sundara look good on a stand, they sound great (I think they might benefit more from EQ than the 560s, but all headphones benefit form EQ), sometimes I can wear them all day and not feel any discomfort but I would give the edge in comfort to the 560s (though some people don't like the clamp force - I don't have a wide head so not much of an issue - on the other hand some find Sundara pads to be small - I don't have big ears so that's also not an issue). The Sundara are more open, meaning they leak more sound (I mean, both are open-back but they just do), perhaps that and more energy on the top end give them a more "airy" feel (to borrow a poor audiophile term that means little to nothing objectively), I prefer them for live stuff and classical.
I haven't heard the HE400Se in the most recent iteration - just have no reason to buy it - but it seems to be really good - a cheaper alternative to the Sundara. It also seems to be the best bet for someone starting out or just looking for good headphones without breaking the bank. The cables are easy to replace without spending much as well.
Now, it would be good for you to know what you prefer when it comes to sound and how your preferences deviate from something like the Harman target etc. You could then make much of the judgment based on the measurements - e.g you might like more or less bass than the target, more or less treble etc. My preferences align with the Harman target well, so I'll like stuff that adheres to the target better - it might not be the case for you. Regardless of your preferences, my strong suggestion is to get the cleanest possible audio-chain and a pair of neutral sounding headphones with low distortion - then EQ to preference.
I just don't see any reason to buy any other open-backs in the range between this and the stuff higher up, e.g. Senn HD800s - and by then diminishing returns have come and gone. Perhaps a used HD800 with EQ if you can get a good price. Obviously, it depends on what you priorities are - if it's purely sound quality - you can get that under 300 GBP no problems. If it's to own something expensive, have particular look, materials, bragging rights, collecting... then obviously the range is open.
I've personally had the Focal Clears - sold them and never regretted it - consider all 3 up there better headphones - even if there's a whole crew of Focal lovers who might react to this.