Thank you for your question..
If the company has not started trading as yet, there is no need to file a CT600 for this company.
The first set of accounts would be for the period 9 Jul 2015 to 8 Jul 2016, had the company started to trade on date of incorporation.
As far as Companies House is concerned, you will have to file a set of Dormant Company accounts after 31 Jul 2016. It is a simple process. You can use Companies House web filing service and opt for dormant accounts.
You should have completed a Form CT41G. More information on this can be found here
I hope this is helpful and answers your question.
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