Am setting up a new company on QuickBooks but am interested in confirming that I can file the accounts directly to Companies House through the software. Please confirm that this is possible and if so how to do it?
This is not possible I think. You can't even file accounts (in the correct form) to HMRC from Quick Books (online or desktop), so how this could be done to Companies House is no easier. However, the format for Companies House is merely for a balance sheet (with appropriate notes) and should not take you longer than (say) 20 minutes on the Companies House website.
I'm inclined to agree with @Mollcons. I'm only new to QuickBooks Online, but I've used QuickBooks Desktop for years. So far I've not seen a whole lot that Online can do that Desktop couldn't and I've certainly never submitted our Companies House returns using QB Desktop. I don't even see how it could do that since it doesn't contain the kinds of information the CH return requires -- things like number of issued shares, share transfers, names and addresses of Directors, and so on.
As I say, that's all for the desktop version, but I'm pretty sure QBO is the same.