Britain's opposition Labor Party jumped to a 14-point lead over Prime Minister Margaret Thatcher's governing Conservative Party among voters questioned in an opinion poll. The survey follows the trouncing of the Conservatives by Labor in recent European Parliament elections. Labor won its first national election victory since 1974 in the June 15 vote. The Observer-Harris poll, conducted last week, showed Labor with the support of 48% of those questioned and the Conservatives with 34%. The environmental Greens party, which also scored well in the European Parliament balloting, held the support of 8%, while the centrist Social and Liberal Democrats fell to 6%.