I assume you're referring to a sales invoice which you issued back in February 2009 and this invoice hasn't been paid by your customer. If you used cash accounting for VAT then this wouldn't be a problem as you wouldn't have paid the VAT over as you didn't receive the cash. However, if you use invoice accounting for VAT then you have to treat the invoice as a bad debt and write it back, claiming back the VAT you paid when you issued the invoice. HMRC prefer you to wait six months after issuing the invoice before claiming the bad debt relief. This is a link to the relevant page on HMRC's site http://www.hmrc.gov.uk/vat/managing/reclaiming/bad-debts.htm
It doesn't matter if the debtor is still trading or not.
Hope this helps - Give me a call on 0161 621 9973 if you'd like to discuss this further