Offshore savings income while non resident for employment

My client left the UK to take up employment overseas during the 2006/07 tax year. The employment ended and they returned during the 2008/09 tax year. So they have one full tax year out sude the UK resulting in split year treatment in the other 2 years. Therefore no UK income tax on the employment income.

The offshore salary was being paid into an offshore bank account. It is the tax treatment of the interest on that account that concerns me. In the year of return what is the treatment of the offshore bank interest.

Is it all taxable?

Is it time apportioned with the pre return not taxable and the post return taxable?

Do we have to establish the dates it was paid with the pre return being not taxable and the post return taxable?

Thanks