It’s quite possible we don’t recognise that prefix and are excluding it in our validation, even though it may be a perfectly valid company number. I’ve logged it for review so we shall take a look shortly and report back.
We’ve contacted Companies House but I don’t believe IP companies can be queried using their XML service. In the next release we will allow for IP companies to be entered into QuickFile but it doesn’t look like it will automatically pull in the filing dates as it does for other company types.
Companies House just replied and confirmed that IP companies aren’t accessible via their data service. However we will as discussed allow those companies numbers to be saved on our side.