WE'RE in a beer garden in Colinton Village, a few doors from where the Tories used to have a parliamentary office, and SNP candidate Joanna Cherry is fielding questions about how unlikely it seems that she could be taking her party from a poor fourth place five years ago to victory next month.

The Labour candidate has been expressing surprise about a recent poll from Lord Ashcroft putting the SNP well clear out in front of Labour in the Edinburgh South West seat being relinquished by Alistair Darling, as this doesn't match his own party's canvassing, I say.

Ms Cherry's eyebrows rise and she suppresses a smile as she looks across the table to her election agent. And the Conservative candidate, I continue, says it's a two-horse race between him and Labour . . . Her eyebrows shoot higher and lips purse to avoid laughing.

The advocate is tough, as you might expect of someone who became one of the country's first special sex case prosecutors and who has represented the Scottish Government before the UK Supreme Court. But she also has a mischievous streak.

How is she getting on in, say, true blue parts of Balerno? "What they are looking for is a strong articulate MP, someone who is no shrinking violet. In this seat they have a history of voting for high profile lawyers - Malcolm Rifkind, Lynda Clarke, Alistair Darling . . ." I point out that her Conservative opponent, Gordon Lindhurst, is also an advocate. "Ah," she points out with a twinkle, "but he's not a QC."

The recent Ashcroft poll in the constituency put the SNP on an astounding 40 per cent, up from just 12 per cent at the last General Election, Labour at 27 per cent (down from 43 per cent), the Conservatives on 19 per cent (from 25 per cent), the Liberal Democrats on 4 per cent (from 12 per cent) and others on 9 per cent (up from 3 per cent).

None of this is out of line with general polling across the country, nor is it surprising given what happened at the last Holyrood election where one of the shocks of the night was Gordon MacDonald taking Pentlands from the former Tory leader, the late David McLetchie, while the SNP also captured Edinburgh Central, which makes up another part of the Westminster constituency.

All of this points to a tough night for Daniel Farthing-Sykes of the LibDems, Richard Doherty of the Greens and Richard Lucas of Ukip as they contest the scraps and fight to save deposits.

The man with most to lose, specifically the 8447 majority bequeathed by Darling, is veteran Labour councillor Ricky Henderson. After 16 years in the City Chambers he is now convener of the health, social work and housing committee so we meet in the Royal Mile between meetings.

A former telephone engineer, he became an official of the Communication Workers Union and was first elected to the Parkhead ward in the Sighthill area, but his Pentland Hills ward now encompasses many of the more affluent parts of the constituency.

He should be well award of the March of the SNP, given that he stood in the Holyrood seat, but he continues to express puzzlement about that Ashcroft poll. "It's going well for us. We are doing a lot of door-knocking and street stalls and the responses we are getting have been pretty good. I don't know if surprise was the right word to use about the poll. It was more disappointment that it seemed to reflect what was coming back from polls elsewhere. It doesn't match what we are finding locally. I'm not suggesting it was inaccurate but it might be down the the methodology of the poll because our returns are looking pretty good."

He insists that when he cuts through the Nationalists' argument about standing up for Scotland and points to tangible Labour policies people like what they hear. As for the effect of Alistair Darling heading Better Together and Labour working within that with the Conservatives, he says it's raised by some political activists but not by ordinary voters.

Out at the Corn Exchange complex Gordon Lindhurst is dismissive of the Ashcroft findings and insists he is in a two horse race with Labour who, losing the high profile of someone like Alistair Darling, are vulnerable to a Tory comeback. The SNP will slip back to former General Election levels, he claims, adding: "How Ashcroft decided on which thousand voters to poll is up to him."

Lindhurst, who lives in the constituency, first stood for the Tories in Linlithgow in 1999 and contested the high profile by-election in Livingston in 2005 following the death of Robin Cook. He insists: "Conservative voters like what the Government has done and our vote is solid. If Labour votes desert to the SNP we will be the ones to benefit from that."