On my trips to London I saw a few Subarus... ones I remember...
M6 South - Tuesday between 3pm and 4pm,
Silver classic at the Toll junction, heading down M6 rather than Toll.
Blue Blob or Hawk in slow lane saving fuel
A14 East - Sunday between 2pm and 3pm,
Silver Legacy
M6 North - Sunday between 10pm and 11pm,
Silver classic at Burger King services just after Junction 14