Trustees of the Alliance Boots pension fund, who may have the power to derail the group's acquisition by Kohlberg Kravis Roberts, have demanded a payment of £1bn (€1.5bn) from the buyout group to cover the fund's deficit.

KKR, together with Boots deputy chairman Stefano Pessina, tabled a £11.39-a-share bid for Alliance Boots, valuing it at £11bn, in late April. If successful the buyout would be one of the largest on record in Europe.