Well, I've just listened to the first movement and I'm not quite sure what to think. I'm not feeling coherent enough to bother typing a full review so I'll just make some brief points as they come to me.
1) My first impression is that this is... a fairly confused work. There are moments that clearly make reference to English composers around the turn of the 20th century as you noted. But then, there are clear references to the Classical era. This is not a fundamental problem in itself. Prokofiev, Shostakovich, and Britten all come to mind as composers who were able to convincingly pull off this 'neoclassicism' (at least, sometimes.) But the way you handle it is. For starters, you never seem to consciously exploit this incongruity. Rather, you try, entirely straight-faced, to weld these elements together and the result is... unconvincing. The 'bridge' theme is the biggest offender of this. It just sounds entirely unrelated to the rest of the work and the fact that you repeat it at a few given points with basically no alteration doesn't help. like I said, I've only listened to the first movement so I don't know if this problem is elaborated on or handled better in the next few movements but as it stands, it just doesn't work for me in the context of this movement. And just to avoid what I think will be the most likely reaction, I'm not saying this because I hate all classical music pre-20th century. Beethoven is one of my favorite composers and one whom I consider one of the my biggest influences.
2) I take some issue with this being labeled as a 'sonata-allegro' form. As I'm sure you know, sonata-allegro refers to not so much a textbook structure as a style of musical thought a manner of handling musical material. The basic components are first a section that highlights two contrasting tonal areas. A tonality and its 'dominant' (though, for all intents and purposes, this is more any tonal area which increases the harmonic tension of the form rather than the actual 'dominant' as Beethoven was perfectly capable of using mediants in place of the actual dominant.) Then a section that further plays up the contrast between these areas before achieving a climax that resolves into a third section which repeats the first section on face value but, on a more fundamental level, shows the two tonal areas to have been resolved into one.
Now, I'm going through all of this because I feel your piece lacks a few of these necessary ingredients. First off, there is never any sense of a 'dominant' in my opinion. If anything, your second subject seems to function as a subdominant area. Now, I know that Schubert and Brahms both attempted this same procedure in their 'sonata' forms but... they suffer the same issue really. There is a slackening in harmonic tension rather than an increase and this effects the intended dramatic structure quite a bit.
Second off, the almost demanded climax of the development section never occurs either. The 'recapitulation' seems to occur right after the second cadenza (or right around there, you do flow into it effortlessly) yet, when it does, it feels... arbitrary. There was no real climax to speak of. The cadenza occurs when the tension in the piece seems to be at an almost full time low. And the cadenza does nothing to elevate this energy level. Now, I know it was pretty common-practice in Mendelssohn to have the recapitulation start at the point of lowest tension rather than highest and it is possible for the recapitulation to work on this level with amazing results. But Mendelssohn typically achieved this by having the music reach a near stasis and then slowly building back up to its vibrant first subject. You don't do this. You recapitulate only the second subject and never state the opening theme in its prototypical form.
In fact, that becomes the biggest issue because there is never a sense of resolution. The entire piece starts with a fair amount of energy and then it sort of just declines. None of what happens in this movement other than the very basic skeleton of Theme - development - return can be considered a sonata-allegro. Nor do I think the material is necessarily conducive to one.
All of that being said, that doesn't make the structure bad in itself. By no means am I trying to tell you that you should conform to sonata form in order for this piece to be successful. I'm just trying to suggest that it isn't one and the fact that you seem to be rather preoccupied with filling in all the textbook requirements of the forms hurts it overall. I think the material you have justifies something more akin to a rhapsody on two themes or something of an arch form.
3) Your rhythmic sense is very dull. While your harmonic language borders on early 20th century at quite a few moments, your rhythmic language is dead stuck in the early 18th century. Almost the entire piece is written in basically straight 4/4 without even much in the way of syncopation. Hell, you rarely seem to stray away from traditional quadruplets without even so much as triplets most of the time (and when they are employed, it's mostly for a 'decorative' effect of landing on a firm strong beat.) In particular, this seems to hurt your second theme which seems to demand a more 'weightless', transparent quality than regularly pulsed quarter notes can provide. Even Mozart and Haydn were, at times, capable of negating (or at least, blurring) a sense of meter at times. Now, keep in mind that I'm something of a snob when it comes to rhythm and even most 20th century composers, in my honest opinion, don't have a very good sense of rhythm. But I still feel that a more fluid sense of rhythm could inject a lot of energy into this piece.
4) I also have some issue with your timbral and textural sense. For 95% of this piece, the piano and violin play together with the piano almost always being the accompanying voice. There are few moments where the piano is prominent and even fewer where it plays alone (actually, I'm not sure if it ever does for more than about five seconds.) Nor is the piano particularly contrapuntally interesting at most times. This constant effect of violin = principal voice, piano = chords and subsidiary voices leads to monotony. Especially when the hands of the piano part are kept in very standard ranges and are both almost always playing which creates an almost constant texture. For that matter, the violin is never really called to do anything out of the ordinary either. The range is pretty standards for the most part. There are few double or triple stops that aren't octaves. There is not a single note of pizzicato. And the violin, to my recollection, doesn't even have much in the way of implied counterpoint. I feel as if there a ton of musical effects and textures that were not exploited in this piece. And granted, most may have been of no interest to you given the relatively conservative idiom but there are definitely times where I feel it warranted.
5) On a more positive note, I do feel this piece has a fair amount of potential. There are moments where the harmony is rather pretty and I'm pretty sure I can see what you were aiming for in this. Your economy of material is also commendable and you definitely have no issue in handling classical development. The themes are both strong in themselves and, as far as the thematic spectrum goes, it was never really dull. I don't feel as though much tension was played up with them as there could have been but it certainly could've been handled much worse. ]
If I have the patience, I may type out a 'review' for the next two movements but don't hold me to that. I'm sorry for being so negative (more negative than I expected to be) but I feel the most constructive criticisms are usually this way. Glad to see you're still writing.