In some circumstances, a company will continue to be shown as 'active' on the Companies House register for at least a year after going into voluntary liquidation. This is from the Companies House website:
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Whatever the proceeding, the company is insolvent and will eventually go off the Register, won�t it?
In a members� voluntary liquidation, the directors swear a statement, known as a declaration of solvency, to say the company will be able to pay all its debts within a period not exceeding twelve months. The company would not be 'insolvent'. Only liquidations result in the company being automatically dissolved. It is possible, following the conclusion of a receivership, administration or corporate voluntary arrangement, for a company to remain on the live register and continue trading."
As StarskyH suggests, the Gazette might be the best place to look for information. However, a notice also has to be placed in a local newspaper in the area in which the firm is trading. Further information is under 'Who must be told that a company is in administration?' in Chapter 3, Part 1, Section 4, here:
http://www.companieshouse.gov.uk/about/gbhtml/ gbw1.shtml
Chris