There is a tax allowance that has had a low takeup, and does not seem to be widely known about. It is called the Marriage Allowance, and is for couples (including pensioners) where one partner pays standard rate income tax and the other is a non-taxpayer.
It can be claimed in the following circumstances:
If you qualify, the lower earner can transfer part of their unused income tax allowance to the higher earner. As an example, this would have reduced their income tax by up to £230 in the tax year 2017-18. The allowance can be backdated, and the sooner the application is made, the earlier the tax year it can be backdated to.
More information is in the following link to The Guardian:
www.theguardian.com/money/2017/sep/23/230-pounds-marriage-allowance-hasnt-been-claimed.
Claiming is quick and easy. The allowance can be claimed online here:
www.gov.uk/apply-marriage-allowance.