Search over 2.7 million UK companies registered with the United Kingdom's registrar of companies (the name of which cannot be mentioned here).
This app is not the official app, but uses the official API of the United Kingdom's registrar of companies (the name of which cannot be mentioned here).
Compared to the official app you can access much more data, including but not limited to charges, insolvency, owner data, much more details and cross references.

No need to register.
Store your most frequently viewed companies in your favourites.

Known issues:
The filter menu text is invisible in landscape mode on some tablets (e.g. Nexus 9). This seems to be an Android OS issue.