Married couple tax relief on pension AVCs - transferable or not?

What_time_is_it

Thanks for the clarification.
She pays into a DB scheme from Net Pay and pays less PAYE tax on that.
The AVCs are additional contributions, taken at source (salary) but NOT via salary sacrifice and not reducing the PAYE tax she pays on her payslip. i.e. If she pays £500 AVC contribution, then her monthly take home pay goes down by exactly £500.

Dazed_and_C0nfused

What_time_is_it said:

Thanks for the clarification.
She pays into a DB scheme from Net Pay and pays less PAYE tax on that.
The AVCs are additional contributions, taken at source (salary) but NOT via salary sacrifice and not reducing the PAYE tax she pays on her payslip. i.e. If she pays £500 AVC contribution, then her monthly take home pay goes down by exactly £500.

Does the £500 have 25% added to it by the pension company so she sees £625 in her pension fund?

That is "relief at source" and her PAYE tax amount is irrelevant to this pension tax relief.

p00hsticks

What_time_is_it said:

Does the married couple tax relief (not sure what it's called) apply on AVC contributions that are paid from salary but NOT taxed at source?

Just for clarity, as some of the other posters have adopted your nomenclature, I believe that the tax break you are asking about, and that this thread is discussing, is actually called the Marriage Allowance. 

https://www.gov.uk/marriage-allowance

There is an earlier  separate (more generous) allowance called the Married Couples Allowance, but to qualify for that at least one of the spouses has to have been born before 6th April 1935, so there aren't that many couples eligible for it

https://www.gov.uk/married-couples-allowance