If you own a property jointly with your spouse 50:50, you will need to alter the capital ownership first. This alteration will apply for capital gains tax also. If the proportion of mortgage debt moving with the ownership is more than £125,000 then Stamp Duty Land Tax will apply but not at the extra 3% rates.
You then need to submit a form 17 to HMRC (with proof of change of % ownership) to elect to be taxed in accordance with the ownership rather than the 50:50 default. Without a form 17, jointly owned property will automatically be taxed 50:50 regardless of ownership. This cannot be backdated. The election remains in place until the ownership changes again.
If your spouse owns only 1% of the capital in a property, the 50:50 default will apply and they can be taxed on 50% of the rental profit.