SDLTM34090 | Special provisions relating to partnerships: Partnership Interests: application of provisions about exchanges etc.
From HM Revenue & Customs · Stamp Duty Land Tax Manual
Where a partner acquires an interest in a partnership and the consideration for that interest is the transfer of land to an existing partner (as distinct from the partnership), the interest in the partnership shall be treated as a major interest in land (for the purposes of FA03 Sch4 Para 4(5)) if the relevant partnership property includes a major interest in land.