Hi. My name is*****'m looking at your question now and will post my answer or ask for more information here in a short while.
Unless the account is in joint names, the interest is yours for tax purpsoes andf should be disclosed in your tax returns as such. If the account was in jount names, the division would be 50:50 unless the ownership proportions of the asset were other than 50:50 and HMRC were informed via a joint declaration using form 17.
I hope this helps but let me know if you have any further questions.