US private equity group Advent International faces having to claw back up to €80m from investors and partners following an arbitration ruling on a Bulgarian telecoms deal it completed almost 10 years ago, according to four people familiar with the situation. Negotiations continue over the precise amount.

When Viva Ventures, a special-purpose investment vehicle set up by Advent, bought a 65% stake in BTC from the Bulgarian government in 2004 for about €230m, the agreement included a clause which entitled the state to 10% of the resale proceeds over €300m, according to local media reports.