There's a lot to digest here however, David G, the concept of fraudulent preference has been replaced by a simple preference. If the over-riding purpose of the transaction is to prefer the creditor benefiting from it, then it is a preference and can be overturned. If the bank has a debenture (which appears likely, but I have not read the thread in fine detail), and there are sufficient funds to pay the preferential debts (holiday pay and up to £800 per employee wages arrears), the lion's share of the surplus will fall into the debenture and so a payment of £90,000 out of receipts of £1.4m is, in practical terms, unlikely to fall foul of the rules.
That said, and assuming that the bank does not want to appoint its own administrator under its debenture, the "proper" way of dealing with the matter would be to collect in the debts and allow the proposed IP to clear any cheques through a designated client account. The funds in there would be held for the benefit of the liquidation. It would be for the liquidator to assess the validity of the debenture (banks do foul up) and then distribute the funds in the statutory order of priority. In the meantime, the guarantor should take specialist legal advice on the enforceability of the guarantee and open a dialogue with the bank. It is unlikely the bank would commence proceedings until the outcome of the liquidation could be assessed with any degree of certainty. The bank will of course have to go through its normal procedures of calling up the guarantee and requiring payment but usually banks are prepared to be sensible about these things.
As regards doing deals and making compromises with customers, strictly-speaking this should be a job for the liquidator, although the directors remain in executive control of the company until it is formally in liquidation. My recommendation would be to consult the IP before agreeing any compromise - after all, that it what he is being paid for! At my company we use the services of a couple of excellent quantity surveyors who have "been around the block" once or twice and know all the tricks contractors and other customers use to try to avoid paying their debts when their (sub)contractor goes bust. They usually get pretty good results.