HMRC marriage allowance works by reducing the personal allowance of the donor spouse or civil partner.

Some households can use a 'backdating' method to get a massively boosted £13,830 Personal Allowance fully tax-free.

The tax-free Personal Allowance has remained frozen for several years and will continue at its modest £12,570 threshold for at least another five years following the government's latest extension, ...

Households can increase their tax-free Personal Allowance and will get a cheque too if they're eligible to back-claim.