If you accept the 50/50, you will lose your policy excess (or 50% thereof depending on the damage) and assuming that this is your only claim, should not see a problem with your no claims bonus - depending on what the terms of your policy are.
If you decide to fight the matter, it will ultimately end up in the small claims court. Most insurance companies will, if liability is disputed, pay for legal advice and a barrister to represent you at court and it sounds as if yours would, but check this. If not, small claims is designed for you to be able to represent yourself.
If it does go the small claims court can I urge you to 1) put in the fullest statement you can concerning the facts of the accident (include details of speed, weather conditions, traffic in opposite direction, skid marks or lack thereof and EXACTLY what you did/saw etc etc - don't be fobbed off with the statements that you are asked to fill in - give as much detail as possible and check it very carefully 2) include a diagram drawn as neatly to scale as possible, 3) include photos of the location. Depending on who issues the claim it is for them to prove on the balance of probabilities. However, in reality, what it will come down to who the judge believes.
Unfortunately, judges tend not to take into account too much what was said after the accident on the basis that people very often say daft things immediately after an accident. Your uncle's lack of independence does not matter as such, but he did not actually witness the prang.
So his evidence is ikely to be deemed largely irrelevant by the judge.
You also have to take into account whether you want the stress and hassle of taking this to court.