"My logic is very much that assets can be easily transferred between spouses."
Yes they can, Geoff, so the key to your problem is to find a way of transferring it. I don't see how the taxman can solve your problem whilst the loan is in your name with interest payments being paid to you. I also don't see why the loan platform company/site wouldn't accept an instruction from you transferring the loan rights to your wife. After all, what would happen if you died and had left all your assets to her?
You are right that HMRC will pick up any anomalies between your declared income and returns submitted by the institutions paying you interest. A couple of years ago, my wife received notification that she was to be subject to a Revenue investigation and, on enquiry, it turned out to be in respect of interest paid on a Trust account where she was first-named Trustee. It was easily solved by showing that the interest had been declared and taxed appropriately within the Trust, but the point is that in this computerised world any mismatch will be flagged up immediately and when HMRC comes to call, you can't just say 'it's hers not mine' without supporting evidence.