I have a client who started using my services as a sole trader in retail. I've done all his bookkeeping this year, registered him for VAT etc. even submitted his self assessment only to get a phone call today to say his wife got a letter from HMRC to remind her about her partnership tax return.
It seems, from what I can gather, that his wife registered the business as a partnership with both being partners but no one told me until today.
My question, what do I do. I have submitted his self assessment this year as a sole trader.
I would call HMRC helpline for their advice. (sounds like you will need to do an amended return)
At the end of the day it is self assessment so although you have submitted it i assume you will have got the clients written authority to submit what you submitted. So it is their mistake at the end of the day.
You can only work with the information you have at the time.