Both David Cameron and Ruth Davidson had the same message for their party conference in Edinburgh yesterday - a vote for the SNP is a vote for Labour - but it is the differences between the Prime Minister and the party's leader in Scotland that matter.

Indeed, those differences may hold the key to the Conservatives' performance at the general election in what is an unsettling and unpredictable time for the Conservative party and Scottish politics in general.

The differences between Mr Cameron and Ms Davidson run fairly deep, especially for many Scottish voters. Mr Cameron is an Eton-educated Englishman whose approval ratings are much lower here than they are down south; Ms Davidson, as her rather slick party broadcast demonstrated last week, is a comprehensive girl from Fife who is seen, by Tory voters and non-Tory voters alike, as likeable and able.

Mr Cameron and Ms Davidson also enjoyed very different referendums. Whereas the Prime Minister was widely seen to have used the result for party political advantage by proposing English votes for English laws on the morning after the referendum, Ms Davidson won credit by sensing the mood in Scotland and reversing her original outright opposition to further devolution, although some characterised her change of heart as an embarrassing U-turn. Whatever your interpretation, she confronted the truth that, although the majority of Scots do not want independence, they do want a considerably stronger voice for Holyrood.

Ms Davidson has also demonstrated her willingness to strike a different tone to the Tory party down south. Earlier this year, for example, when the flags over Downing Street and other public buildings were lowered as a mark of respect for Saudi's King Abdullah, Ms Davidson called it a pile of nonsense. It was a demonstration of independent thinking that endeared her further to voters who have warmed to her personally without necessarily identifying with the Conservatives.

This personal popularity could help the Conservative party retain its single MP in Scotland, although it is unlikely to spell any serious political revival. The Scottish leader used her speech yesterday to propose giving parents more control over their children's education by opting out of local authority control and that is interesting territory for her and a chance perhaps to carve out a right-of-centre USP in Scottish politics while all the other parties essentially argue over the same ground.

However, Conservatism remains a minority interest in Scotland kept in its place by the long memories of many Scots for Thatcherism, and Ms Davidson was over-optimistic when she declared that the referendum result could mark a beginning of a revival in the Conservative vote in Scotland. Despite her warning yesterday that a vote for the SNP is a vote for Labour, her party also faces the possibility of being wounded by tactical voting.

The problem is this: the latest polls may show Scottish support for the Tories at around 15 per cent, which is pretty much the same level of support they have attracted since the massive crash in their votes in the mid to late nineties, but the resilience of the SNP vote continues and that poses a problem for Tory-minded voters. If they decide to vote Labour to keep the SNP out, that could seriously squeeze the Conservative vote.

Ms Davidson insisted yesterday her vote was holding up against such tactical talk, but her prospects of progressing much beyond 15 per cent are defined by how much Scotland appears to have been changed by the referendum. The Yes campaign did not win, but it did outline progressive, left of centre ideas in a country that is, broadly speaking, further to the left than England. On that landscape, it is hard to see where even Ruth Davidson's Conservative party can progress; indeed, the change to the landscape has been so profound that, in May, she may even be relieved to hold their current position.