Employing a Bulgarian or Romanian National
You need to read this document. It explains about the different types of card, plus about work permits.
Having looked at it, my thoughts are:
A card/certificate is issued for a specific employment. Therefore a new card would be needed.
Nanny I feel should fit the category of "Domestic workers in a private household" thus you as the employer won't need to apply for a work permit.
The Yellow Certificate is issued to: "the self employed, self sufficient persons and students. The certificate will indicate in which way the holder is exercising their treaty right"
"Purple Work Cards (aka Accession worker cards.) These are issued to those Romanian and Bulgarian nationals seeking employment in one of the categories listed in section 1." - given that "Domestic workers in a private household" is listed in section 1, how come this person does not have a Purple card? Why do they have a Yellow card?
I think the yellow card is not sufficient.
I would agree, though feel you do need to check this out with UKBA (0114 207 4074). Given that the person would be changing job, maybe UKBA will issue a Purple card for this new job.
The Yellow certificate may mean that they applied to come to the UK as a self-employed person, or as a student, or self-sufficient. So it will depend on what specifically is written on the certificate. Have you seen the certificate? Did it say that it was issued due to the person being self-employed?
According to BR1 the certificate DOES NOT confirm employment status. Therefore even though it may have been issued for someone who is self-employed, given that they are now applying for a nanny job, the card DOES NOT in my view indicate that the nanny job can be done as self employed.
If you employ the person and they are later found to be holding the wrong type of certificate, then you could face a fine of £5000.
"An employer who employs Romanians or Bulgarians working illegally will be liable to prosecution in a Magistrates court under the Accession (Immigration and Worker Authorisation) Regulations 2006. On conviction, the employer will be liable for a fine of up to £5,000. If the fine is not paid, the court can use bailiffs to seize goods and sell them. Alternatively, they can order the employer to be sent to prison."
Thus you do need to check this all out with UKBA and confirm that this person will be getting a new card (given that they are changing job) and that the card being issued is of the right type to enable them to do the job.
Do I have to register as an employer + pay taxes as an employer?
Yes, you are advised to operate PAYE. You will need to register as an employer and pay employers NI. You will also need to deduct employee NI and Employee income tax from your employees gross salary.
While the person may have been self-employed for other work, it does not mean they will be for the job you are offering. Is this a full-time nanny position... or are you just wanting a nanny on various different occasions?
Does she need additionnal paper from Home Office?
Yes, from how I read the employer guidance, she needs to tell UKBA that she is going to change jobs and needs a new card issued.
I feel she needs to tell UKBA that she will be a worker, not self-employed. Then with luck UKBA will issue a Purple Card.
Ah... there's a problem though. BR3 says the following for a "Domestic Worker in a Private Household":
"You must enclose with this application a letter from your employer setting out the details of your employment and confirming that you have been employed by your employer overseas (unless you are being employed in a diplomatic household) for at least one year as a domestic worker under the same roof as your employer, or in a household that your employer uses on a regular basis. If you will be employed as a private servant of a member of staff of a diplomatic or consular mission, your employer?s letter should confirm that he or she enjoys privileges and immunity within the meaning of the Vienna Convention on Diplomatic and Consular Relations."
So that is probably why she hasn't entered the UK under the "Domestic Worker in a Private Household" category.
She could apply under the Au Pair category if she meets the conditions... max working time is 5 hours per day.
So assuming the job you are offering is for more than 5 hours per day, then she has to use the self-employed card. Problem is, nannies would not usually be self-employed given employee/employer relationship that is typical in a nanny job.
All very messy... could you not just hire someone else?