Lansdowne Partners said the shocking performance of BT in the wake of a profit warning and a £530m accounting black hole in its Italian division, together with the floundering of satellite firm Inmarsat reduced the overall value of Lansdowne's assets under management by 1.3 per cent and 0.9 per cent respectively.
BT was sent into freefall on 24 January after the revelations about its Italian arm: after a 20 per cent dive in its share price, £8bn was wiped off the firm's market cap.
Read more: BT's overseas operations put under review
Lansdowne, which had managed $20bn (£16bn) of investments in the middle of last year, saw its main $9.3bn developed markets fund drop 15 per cent in 2016. And according to an investor letter seen by Reuters, the same fund fell a further 2.9 per cent in January.
But Lansdowne chairman Stuart Roden said in the letter it was time for the sector to stop making excuses for failing to deliver.