Wendy Alexander's campaign team registered an illegal donation in the name of a Glasgow-based company at the eleventh hour after realising they might have already broken electoral law.

The Labour leader's team had been under the impression that donations under £1000, regardless of origin, were permissable, including the £950 from Jersey-based Paul Green that has rocked her leadership for the past six weeks.

However, after they realised they had misinterpreted electoral law, the cash was instead registered in the name of Combined Property Services (CPS).

Alexander and her team are being investigated by the Electoral Commission after admitting they accepted the donation as part of her leadership campaign.

Her campaign members have consistently declined to answer questions on why and when CPS was first named as the source of the Green cash.

Charlie Gordon, the Labour MSP who solicited Green's cheque, said in November: "I handed the donation to the campaign team, and conveyed to them that it was under the auspices of CPS." It is understood Gordon is now claiming he made an error in saying he initially told the campaign the cheque was from CPS.

The Sunday Herald understands the Commission is aware of Alexander's team's apparent ignorance of the law.

Correspondence between Alexander's office and Gordon, which started in October, focused on the legality of the donation but made no mention of CPS.

Alexander is set to break her silence when she is interviewed on the BBC's politics show today. She is said to be planning a "media fightback" in anticipation of the Electoral Commission's report.