Gigaclear Ltd., a startup building out fiber-optic connections in the UK, has attracted investment commitments for as much as £420 million ($523 million) of equity to fund its race to connect rural homes to high-speed Internet access, according to people familiar with the matter.

The investment will be led by infrastructure investor Equitix Ltd. and will come in phases, the people said, asking not to be identified because the deal isn’t yet public. Gigaclear’s owner, M&G Plc’s infrastructure unit Infracapital, will remain the majority holder after the round, the people said.

Representatives for Gigaclear, Infracapital and Equitix weren’t immediately available for comment.

The investment is a vote of confidence at an increasingly challenging time for British fiber optic startups, which have spent the past few years racking up debt, building out networks to challenge former state monopoly BT Group Plc.