AN internal investigation is under way at the SNP to track down the source of an e-mail which alerted the media to the break-up of the marriage of Michael Russell, the former front bencher, and his relationship with a researcher.

The e-mail sent out to media offices at the weekend was in the name of Jim Welsh and purported to come from an official SNP e-mail address,

But party officials said yesterday that there was no such valid e-mail address within the party and they were satisfied that the only known Jim Welsh in the party locally had nothing to do with spreading the rumour about Mr Russell.

Mr Russell, the SNP's education spokesman in the last Scottish Parliament, lost his seat at the election this month after being placed too low down the party's South of Scotland list.

Senior party sources were stunned late last week to be informed by Mr Russell, 49, that he had separated from his wife after 23 years. He was said to have begun a relationship recently with Eilidh Bateman, 28, who worked as his researcher at the parliament.

A statement was prepared by Mr Russell for release in the event of any inquiries. These swiftly followed when the e-mail tipped off newspapers, saying: ''Do you know the current situation regarding Michael Russell (former MSP) and his ex-secretary . . . if not, you are advised to follow-up.'' Once Mr Russell confirmed that he had separated from his wife, and pleaded for her and their teenage son to be spared intrusion, journalists at the weekend began trying to track down the ''Jim Welsh'' behind the tip-off, along with party officials.

No office-bearers use the address '''' as the official format uses ''''.

A spokeswoman said the party was satisfied that the only Jim Welsh in the local party was not responsible. He was said not to be a particularly long-serving or active member, although he did stand as a council candidate three weeks ago. ''We have spoken to Jim and genuinely believe he had nothing to do with this. We don't know whether whoever did this was trying to get Jim into trouble, or whether they did this to cover their own tracks.

''As this is not an SNP e-mail account this was clearly malicious, but we don't know if it involves an individual with a grudge, someone inside the party, or someone in another party.''