Under English law, the term 'partnership' merely describes the relationship which subsists between two or more persons who carry on business together with a view to profit1. Such a partnership is not a separate legal entity, distinct from the individual partners. The rights and liabilities of a partnership are simply the aggregate of the rights and liabilities of the partners.
A partner is directly interested in each and every asset of his partnership, and participates directly in its profits. Contrast this with a shareholder in a company — he owns an asset (his shareholding) which is quite separate from the assets of the company, and is entitled to participate in the company's profits only to the extent that dividends are declared on his shareholding (see I6.101).
However, that does not mean that a partner's interest in each partnership asset separately forms part of his estate for IHT purposes. It is his partnership share itself which forms part of his estate, that share comprising, broadly: