The 0.05 per cent cut is a 25 per cent reduction on its previous annual management charge.
The firm dexcribed RDR as having been a "watershed moment" for index funds and said it had seen new interest from UK advisers.
From today (8 April) the AMC for single country and regional index funds, including the UK Equity Index fund, is 0.15 per cent. The AMC for core global index funds is 0.25 per cent, including the L&G Emerging Markets Government Bond Index fund.
The reduced charges apply to the 'I' and 'M' unit class of each fund which refer to the nil commission or 'clean' priced units that are available on a range of platforms. The new charges also apply to direct intermediary deals that meet minimum investment levels.
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Simon Pistell, managing director of L&G Investments , said: "Interest in passive investing in the UK has steadily grown over the last two decades and 2013 could be a watershed moment. The RDR and shift to a fee-based advice environment has increased the pressure on advisers to offer greater value and reduce portfolio costs. Some are considering dipping their toes into index funds for the first time, and others are looking at new ways index funds can be used to construct portfolios.
"It's a priority for us to expand the reach of our index funds amongst these financial advisers this year. We'll be launching new products and maintaining our commitment to good value index funds combined with excellent service."

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