When filling out the Affirmation to Marry form (from UK embassy) it requires Mother's name

I am a British National/passport holder born in Britain. My mum is Malaysian (she still holds Malaysian id and passport) although has been resident in UK for 30+yrs and so has pension/nhs etc there.

On her Malaysian ID and passport, she still has her maiden name

Whilst on all UK documents (ie: for banking, tax, pension etc) she has my father's surname

So, which name should I put for her on the Affirmation to Marry form? and how important is the accuracy of this?

It is possible, though unlikely, that the embassy will check, so I'd put the name she uses in the UK.