An instalment of income tax is due to be paid on 31st July. If you are late in paying this instalment, then you will be charged interest at a rate which is currently 3% per year. If you make a part-payment towards the instalment, then this 3% will be charged on the outstanding difference only.
If you cannot pay because other people owe you money, then click here for basic advice on debt collection. As well as adopting a better debt-collection system, you should also know about the Cash Accounting Scheme for VAT if you are VAT-registered and it is relevant.
This instalment is a part-payment of income tax for the tax year running from April 6th 2013 to April 5th 2014, but it is actually based on the known profit of the previous year from April 6th 2012 to April 5th 2013. If your profitability has fallen sharply since the previous year, then you may be able to ask HM Revenue & Customs for a reduced payment on account which is more appropriate to your current financial state. Your accountant will help with this.
You could just send the latest set of business records to your local accountants, and ask for everything to be done quickly so that the latest tax return is submitted and the true final liability, if less than last year, is dealt with fairly from your point of view. If you make a part-payment of income tax in the meantime, and happen to have overpaid, then any excess will be refunded to you by HM Revenue & Customs.
If we may be allowed a mention, a firm of accountants such as David Porthouse & Co, if asked, will process your records as quickly as possible using the latest technology such as optical character recognition to scan your bank statements.