The issue began when HMRC made my client aware of the default requirement to treat income from joint properties as 50/50 for married couples.

HMRC was quite correct, 100% of the income from a property my client owned jointly with her husband, had been declared in his return for 20 years plus. In addition, no election had ever been made to apportion the property differently.

So, we had a scenario whereby the husband (a higher rate taxpayer) had always declared all the income from the property in question and the wife (a basic rate taxpayer) had never declared any.