Normal tax treatment is that interest is taxable on each spouses 50:50.
Where, however, their beneficial entitlement to interest (or any other income from a jointly owned asset) is not actually 50:50, they may elect to be taxed on their actual entitlement.
If you can support each spouses beneficial interest to be other than 50:50 then you allocate interest on that basis.
More information on this can be found here
I hope this is helpful and answers your question.
How could I justify beneficial interest? My wife's earnings were significantly lower than mine?
I have yet to complete my tax return for 2013-14. If I was to change the joint accounts to my wife's name only from now (August 2014), would the interest in 2013-14 and 2014-15 be treated as for my wife only?