We have property that we rent out in the uk and from my understanding, you would need to move back into that property for a minimum of 6 months so it is you main residence. The proof you have is all the utility bills to show that sufficent electricity/ gas etc has been used. ( There are ways round this by having all the bills etc in your name including council tax etc, and having someone you trust to move in and pay you cash each month for their rent!)
Double check with the tax office, send them an email, look on their website etc .
If you move back and live in your house again you won't have to pay CGT when you decide to sell (if it is your main residence). If you sell it without moving back in you will have to pay CGT but it will be pro-rated, e.g. if you lived in the house for 7 years and rented it out for 3 you will pay tax on 3/10 of the capital increase, minus a tax free allowance (check latest rules). This can offset against any other losses. This is the general answer but you need to check with an accountant!