(Reuters) -Premier Inn owner Whitbread said on Tuesday that surging costs for labour, utilities and food would eat into margins in the second half, sending its shares down more than 3% despite reporting better-than-expected first-half results. The hotel chain operator swung to a group profit before tax for the six months ended Sept. 1 of 307.4 million pounds ($347.98 million), compared to a loss of 19.3 million pounds a year earlier, with revenue doubling as travel rebounded. Premier Inn UK’s strong trading performance has continued into the third quarter, the company said, with forward bookin…