Hi there and I am sorry to read of your problems.
Whilst insolvency matters are way out of my level of knowledge in any detail, I would suspect that you need to start the ball rolling as soon as possible - although it is likely that you will be some way down the list of creditors should the organisation go bust, I daresay that it will be in your interest to act now.
The route that you should follow would be through the County Court (not an Employment Tribunal, for you are not an 'employee'). On that basis, I would send a Letter Before Action detailing the money due under contract for the provision of your services and enclosing a precise statement of what was due and when, less any payments received and the dates on which they were received. If payment is still not forthcoming, then go through Money Claim Online
HERE and get the Courts working for you.
This is YOUR money and there must be a limit to your patience. They may well be suffering financially, but so are you and you don't have a bank waiting to provide you with a rescue package! If you can get a claim issued and there really is a rescue plan pending by which they will be able to release money to creditors short of going bankrupt then make sure that your claim is one of those which they have to settle first. If you do obtain Judgement against them then they may be rather more keen to settle than to risk you instructing the Court to send bailiffs in to enforce a warrant.
No doubt others with far more experience in this area can advise further, but I wish you good luck and hope that you do get that holiday after all!