All 21 of Vanguard's low-cost mutual funds are available through Cofunds, which, according to financial research firm Fundscape, has a 26 per cent share of the UK market.
Some 12 of the funds are UK-domiciled while the remaining nine are domiciled in Ireland.
Nick Blake, head of retail at Vanguard, said: "Demand for low-cost index funds is growing sharply in the UK. This is a great opportunity for us to reach out to a wider community of advisers and explain the long-term benefits of low-cost investment."

Alastair Conway, sales and marketing director at Cofunds, said: "We're always looking to expand the breadth of funds available to our users so we're extremely pleased to be able to add these much in demand passive instruments to the platform thanks to the introduction of our explicit pricing model."
Cofunds also announced this week that it has reached £45bn in assets under administration on its platform.
It said the rise, from £36bn at the start of the year, was due to strong sales on its investor, wealth and enterprise propositions.
Cofunds chief executive Martin Davis said: "We've continued to grow steadily throughout the year in what have been trying market conditions. The steady stream of mandate wins across both wealth and enterprise segments bear testimony to our robust business model and our commitment to enable to our clients to do more, more easily."