We purchased a commercial property and the bank would only lend to me, the husband, so the mortgage and property is in my name.

The intention from the start was for the property and rental income to be in my wife's name for tax purposes. Is it possible to show the rental income on my wife's return even though she will not be on the deeds or the lease? I vaguely remember that there is a form to send to HMRC to change the split of rental income between people who own property jointly but I don't think it would be possible on this one?

You can only show the rental income on your wife's return if she beneficially owns the property. You can do this by writing out a deed of trust giving her beneficial ownership from now on, and then you will not need to change the names/title of the property on the legal documents. However, I would advise you to discuss all this with your bank, because it may be considered 'mortgage fraud' if you do not. The Form 17 which must be submitted to HMRC is appropriate when the husband owns part of the property and the wife owns the other part (www.hmrc.gov.uk/manuals/tsemmanual/TSEM9810.htm), However, here you are talking about your wife owning the whole property, so Form 17 is not relevant.