At the start of the liquidation process the Liquidator will write to any party who may have a claim against the company asking them to provide particulars of that claim. A formal request to submit claims will also be advertised in the London Gazette, and by any other means (if appropriate). Creditors usually respond very quickly so as not to delay payment, although some larger organisations and HMRC may take some time.
If shareholders require a distribution of funds early in the liquidation a calculation will be made that accounts for all known liabilities. Shareholders will be asked to enter into an indemnity with the Liquidator which requires the repayment of distributed funds in the event of any additional liabilities coming to light. Be assured that indemnities are very rarely enforced.