brakedwell, quite right. The marginal tax rate for those with more than £23k is therefore 30% not 20% as generally believed. For that reason, where possible, additional income in attributed to Mrs PN and not me.
Some trival interest, such as on a Tesco joint clubcard account is then proportioned 50-50 to minimise my tax. We keep this interest to less than £2 so it attracts no tax.
The other thing to ensure is that any payments attracting gift aid continue to be made by, and claimed for, by the higher tax payer even when tax appears to be at 20%!