I contacted Companies House, ECC and Insolvency Service.
Companies House is the agency that is able to postpone the dissolvency. The strike-off letter was sent on November 2013. By default, the original dissolvency would have happened in February 2014. But it didn't. Because people kept objecting to it, it was postponed for a full year. The last letter I sent to the CH was on September 2014.
Here's a direct quote from Finnish ECC from one of the emails:
"I have now consulted England's ECC and they've gotten a response from OpenPandora, stating they have no funds left. ECC UK won't take the matter into their hands, as there's nothing else to be done besides that you can yourself object to the “strike-off”-status or take the matter forward via courts. Additional information with regards to the court process can be found here:
http://www.ecc.fi/fi-FI/oikeudenkaynti/eurooppalainen-vahaisia-vaatimuksia-koskeva-menettely/
But if the company is indeed without funds, the court procedure won't help you to get your money back."
But I still kept going on, looking for alternative ways to proceed. One of those was the Insolvency Service, which can investigate the companies that are suspected of "serious misconduct, fraud or sharp practice in the way a company operates". I gave every bit of info and evidence I could get a hold on. And the last I heard from Insolvency Service, in August 2014:
"We will be considering your complaint and will then decide whether to carry out a formal investigation. As part of that consideration we may contact you to seek more information."
They never contacted again. And as I didn't have any further evidence for Companies House (and they wouldn't (and probably legally can't) agree to postpone the deadline), they continued with the dissolvency. Apparently someone else went a little further, if there are still records of the company in February 2015.
Oh, and as a side note: as far as I know, OP LTD never objected or denied the validity of the claims. They simply stated they were out of funds.