Why Britain might tolerate Germany buying old dreadnoughts

Why would Britain allow Germany's purchase of South American dreadnoughts to go through?

It could justify faster British construction while diverting German resources into modernising an awkward mixed fleet of old ships.

Allowing Germany to buy the ships could serve two Royal Navy interests in this scenario. A visibly larger German fleet would support demands for a new generation of battleships and carriers, including rushed construction alongside King George V-class ships. Germany would meanwhile have to spend resources upgrading a mismatched collection of pre-First World War dreadnoughts. Making those ships operate as a concerted force would consume time, money and effort otherwise available for more effective threats. These are possible strategic incentives within the purchase scenario, without implying a historical British decision to approve such a sale.