Usual disclaimer: I'm neither a financial nor legal professional. If in doubt, consult an expert.
I'm assuming that the aim of this exercise is to minimise the tax paid on your combined rental income. If so, there are two parts to this: transfer to joint ownership, and then inform HMRC.
Given that you already own the property and are married, the simplest change is to add your spouse as an owner, and then arrange for the property to be owned with unequal shares, your spouse having the larger share:
- If the property is mortgaged, your lender will need to be contacted, and your spouse added to the mortgage.
- A Declaration of Trust will be needed, which states that the property is owned by you and your spouse as tenants-in-common, and assigns the larger share to your spouse (e.g. 99% to her, and 1% to you). While it is possible to do this yourself, the internet tends to suggest getting a solicitor to draw it up.
- HMRC Form 17 must be sent to HMRC, along with a certified copy of the Declaration of Trust, informing them that you wish to be taxed on the rental income in proportion to the share of ownership.
- The property's details at the Land Registry will need to be updated to add your spouse, and to include the wording which implies a tenancy in common.
Thereafter, both of you will need to submit tax returns every year, declaring your share of the rental income.
Some other articles on the subject here and here.
If you buy another rental property in the future, it may be more cost effective to buy it through a company set up for the purpose.