$ cat appearances.csv | csvcut -K 1 -c 6 -- | sort | uniq -c | sort -nr
2372 Unknown
1510 Labour Party
1397 Conservative Party
 579 Liberal Party
 117 Scottish National Party
  82 Independent
  65 UK Independence Party
  62 Plaid Cymru
  38 Green Party
  17 Social Democratic and Labour Party
  17 Sinn Féin
  12 Democratic Party (United States)
  11 Ulster Unionist Party
  11 Democratic Unionist Party
   5 Republican Party (United States)
   5 Fine Gael
   4 MeRA25
   3 Labour Party (Ireland)
   2 UK Unionist Party
   2 The Republicans (France)
   2 Solidarity (Scotland)
   2 Scottish Socialist Party
   2 Pakistan Peoples Party
   2 Australian Labor Party
   1 Zimbabwe African National Union
   1 Traditional Unionist Voice
   1 Solidarity–People Before Profit
   1 Socialist Party of America
   1 Progressive Unionist Party
   1 National Party (South Africa)
   1 Liberal Party of Australia
   1 Fianna Fáil
   1 Democratic Alliance (South Africa)
   1 Communist Party of Great Britain
   1 British National Party
   1 Australian Democrats