CREATE TABLE "top_12_fortunes" (
  "rank" real,
  "value" text,
  "name" text,
  "source_of_wealth" text,
  "2007_rank" text
);

Question: What source of wealth has a value of £5726m?
SQL: SELECT "source_of_wealth" FROM "top_12_fortunes" WHERE "value"='£5726m';