london britain main opposition labour party must commit stay european union single market brexit put end prime minister theresa may destructive brexit several lawmakers say sunday begin party annual conference labour lawmakers trade union leaders write open letter leader call jeremy corbyn go current position press part single market transition britain leave march 2019. months stick position little different govern conservative party pursuit clean break eu labour change tack last month say power party would press full access single market transition something could continue beyond watch dismay government use narrow referendum result justify extreme approach brexit lawmakers say letter publish britain observer newspaper conference week labour commit stay single market customs union rule options achieve labour early move aim increase pressure may weaken lose party majority parliament june election need call struggle unite party brexit labour also keenly aware many supporters especially northern central england vote brexit want control immigration many blame stretch public service hospitals school corbyn say prepare government tell bbc listen members labour party want keep close possible tie eu say whether would change party policy instead say believe transitional period full single market access last long necessary offer support continue migration letter labour lawmakers attack conservative party damage promise cut net migration tens thousands labour must clear migrants blame fall wag job insecurity bad house overstretch public service letter say britain must stay eu 's single market brexit labour lawmakers