I need to be flying solo to improve, which oft's instructor seems reluctant to let me do so
I'm sorry but you are in absolutely no position to judge whether you are at a point to go solo. This is entirely the instructors decision as it his name and licence on the endorsement if anything were to go wrong. Instructors are always taught if there is any doubt there is no doubt, and you don't send the student solo.
In fact even as a CPL holder your won't be in a position to judge. You need about 200 hours of instruction to be able to judge effectively whether someone is ready to fly solo.
If your doing extra flights and are on a JAA course there should be an accountability system. I.e if you are doing more hours than the syllabus you are following allows then you will be repeating the lessons until they are satisfactory. Check your records, and if you do not feel you need the repeat speak to the CFI - oh I forgot they don't have a CFI (and therefore shouldn't even be conducting JAA training - I'd call the CAA and ensure they will accept your training - as they have every right not to) However, the CFI will normally side with the instructor as safety NOT your wallet is the priority.
A good flight school will not discuss your fininancial situation when talking about your ability and will just treat you as a student and will send you only when ready etc. The pressures are yours - not the instructors or the schools.
If you worried about the quality of instruction with your FAA instructor ask for a JAA FI - or should have gone to a JAA school with JAA FIs!
Just trying to make you think about the other side of the argument - which either way your financials shouldn't even enter.
PS I don't work for or have never trained at OFT, but have given over 2000 hours instruction.