FTSE muted ahead of Sino-U.S. trade deal; gambling cos slip

(Reuters) - London's main index swung between modest gains and losses on Tuesday, as investors awaited the signing of the Phase 1 U.S.-China trade deal, while gambling firms slipped after Britain banned consumers from using credit cards to gamble.The FTSE 100 rose early in the session but settled to trade flat by 0910 GMT. The FTSE 250 rose 0.2%, driven by a 6% jump in building materials firm Grafton after an upbeat trading update.Ahead of the interim trade deal on Wednesday, news emerged..