An unregistered company is deemed (for the purposes of section 221) unable to pay its debts if there is a creditor, by assignment or otherwise, to whom the company is indebted in a sum exceeding £750 then due and—
the creditor has served on the company, by leaving at its principal place of business, or by delivering to the secretary or some director, manager or principal officer of the company, or by otherwise serving in such manner as the court may approve or direct, a written demand in the prescribed form requiring the company to pay the sum due, and
the company has for 3 weeks after the service of the demand neglected to pay the sum or to secure or compound for it to the creditor's satisfaction.
The money sum for the time being specified in subsection (1) is subject to increase or reduction by regulations under section 417 in Part XV; but no increase in the sum so specified affects any case in which the winding-up petition was presented before the coming into force of the increase.