British South Africa Company v De Beers Consolidated Mines Ltd [1910] 2 Ch 502 is a judicial decision of the English Court of Appeal relating to the conflict of laws, and clogs upon the equity of redemption.

That agreement also contained a provision which granted De Beers the exclusive right to mine diamonds south of the Zambezi river in perpetuity.

BSAC brought proceedings against De Beers in the English courts arguing that the provision for the exclusive mining of diamonds was unenforceable for various different reasons.

The most important of these, for the purposes of the case, was clause 20, which provided: "Nothing in this our charter shall be deemed to authorize the company to set up or grant any monopoly of trade..." The second was an agreement originally dated 20 April 1892 between BSAC and De Beers.

That document essentially memorialised existing indebtedness of BSAC to De Beers and formalised those obligations into mortgage debentures, and increased the amount of the credit advanced to a total of £112,000.

He began by affirming that the provision for the exclusive licence to mine diamonds was clearly part of the mortgage, and was not an independent stipulation.

He accepted that the law of the foreign country would govern the title to land there, but "when an English Court has before it parties to a contract affecting immovables out of the jurisdiction, it will, acting in personam and not in rem, "upon the conscience," as it has been put, "of the person living here," when it finds an equitable right enforceable by a judgment in personam, give effect to that equitable right, and so indirectly affect the interests of the litigants in immovable property abroad.

Before the House of Lords the BSAC added a new lead counsel to their legal team, Sir Robert Finlay KC.

Lord Atkinson reversed the Court of Appeal on different grounds, holdings that the agreement for an exclusive licence to mine diamonds in perpetuity was a separate and independent stipulation from the mortgage, and hence could not constitute a clog on the equity of redemption.

[16] However their Lordships did not disturb the findings of the courts below that (i) the purported grant of an exclusive monopoly was not ultra vires, and (ii) that a clog could arise under an English law security agreement even if the lex situs of the mortgaged property did not recognise the concept of an equity of redemption.

Academically, the case remains cited as good authority by both leading textbooks in the conflict of laws,[2] and in equity.