The stake held by British transport group Stagecoach in mainland toll-road operator Road King Infrastructure has been lifted from 24.78 per cent to 31.2 per cent after the automatic conversion of 418,380 preference shares.

The preference shares, amassed five years ago, were due for conversion into 48.87 million common shares at $8.56 each on Thursday, Road King said.

The conversion price represented an 84.08 per cent premium to yesterday's market close of $4.65, which was up 6.89 per cent from Thursday.