CGT on sale of property previously gifted to spouse

My wife and I have recently sold a rental property (so not our main residence) and there has been a capital gain. My questions are: 1) I originally bought the property, but later gifted 50% of the ownership to my wife. As this was a gift between spouses, no CGT was due. As we've now sold the property, I want to confirm the purchase price my wife should use for reporting CGT should be the price I originally paid for the property, and not the value of the property when I gifted half to her. 2) As my wife and I own the property 50/50, should we each report for CGT half the purchase price, cost of selling, cost of buying, cost of improvements, sale price - that is, we split all the costs and prices equally? 3) My wife and I are both self-employed and don't know how much we will earn in the current tax year, as our income varies month-by-month. For reportung CGT, we can make estimates, but they are likely to be wrong. We will complete self-assessment tax returns later which will have the correct amounts. If we underpay CGT initially on account, will we be charged interest on the balance?

Hi,

1. Yes, it is the value when you originally purchased the property. 
2. You both split everything 50/50.    
3. No, any additional tax due is then dealt with through your Self Assessment return and would fall under the due date of the return. If it is not paid by that due date though, you would be liable for interest at that point

Thank you.