By joining your friends exisiting sole trader business as a partner, you are creating a new entity for VAT registration purposes.
We would therefore recommend that to avoid any VAT issues which may arises for a previous period, you should insist on a new VAT registration from the date you become a partner in the business.
For example, if any VAT errors become evident for the period before you joined, if you continue with the same VAT number you both are equally liable for the VAT debt, even though it was relevant to the period when the business was wholly owned by your friend as a soletrader.
In addition to obtaining a new VAT number, it is also possible to draw up a legal agreement to protect against this problem.
By Jo Nockels
Disclaimer: The information provided is based on current guidance (at date of publication) from HMRC and may be subject to change. Any advice shared here is intended to inform rather than advise. Taxpayer's circumstances do vary and if you feel that the information provided is beneficial it is important that you contact us before implementation. If you take, or do not take action as a result of reading this information, before receiving our written endorsement, we will accept no responsibility for any financial loss incurred.