Companies House has more than halved the time insurance staff have to spend poring over records by transferring its records on to the internet.
The library's new owners, ICC Information, have made most of its 50,000 kilos of records available by electronic mail, cutting document search times from 2 hours to 45 minutes.
Browsers can download files to produce hard copies which are also recognised as evidence by the courts.
The library's original City of London office has also enhanced its service by extending its on-line service hours from 8am to 8pm.
There had been growing concern among firms specialising in mergers and acquisitions that the library's move to Cardiff would cause a decline in service.
Victoria McLean, ICC's head of marketing, said: "Geographic location is no obstacle in the computer age. We are able to meet the needs of businesses wherever they may be based."