P212 CEEFAX 212 Tue 29 May 21:36/12       The Consjtvativj party has challenged all Labour candidates in the European elections to say whether they are in favour of Britain staying in the EEC. Party chairman Mr John Selwyn Gummjt told a press conference today that only six of Labour's 78 candidates were known to bj pro-Common Market. A large Labour group in the European parliament would bj bad for Britain, hj added. Employment Secretary Mr Tom King said 2,500,000 jobs in Britain depended on staying in Europe and more jobs could bj created with future EEC investment.