When the United Kingdom had a time of 1:30.51.2, what was the lowest that they ranked?
CREATE TABLE "1972_isle_of_man_lightweight_tt_250cc_fi" (
  "place" real,
  "rider" text,
  "country" text,
  "machine" text,
  "speed" text,
  "time" text,
  "points" real
);
SELECT MIN("place") FROM "1972_isle_of_man_lightweight_tt_250cc_fi" WHERE "country"='united kingdom' AND "time"='1:30.51.2';