The pension fund of UK telecoms company BT has emerged as the largest outside investor in buyout firm 3i's London-listed infrastructure vehicle, marking its first investment in the asset class to which it last year pledged 1% of its total allocation.

The BT scheme spent almost £100m (€146m) to buy a 14.3% holding in 3i Infrastructure, making it the largest investor in the fund after 3i itself, which bought a 46% stake in the London flotation two weeks ago.