I’ve already published my selection of seats that I think will best illustrate how well or how badly Labour, the Conservatives and the Liberal Democrats fare in the election.

Now I’m turning my attention to three of the smaller parties: Ukip, the Greens, and the SNP.

As with my previous lists, each seat below represents a particular kind of contest, the result of which will serve as a measure of the respective party’s success – or failure.

Ukip

Boston & Skegness

This is often spoke of as Ukip’s best chance of a gain at the general election. The party managed a 9.5% share here in 2010, and needs a gigantic 20% swing to win the seat from the Conservatives. The sitting MP Mark Simmonds is standing down, and an opinion poll commissioned by Ukip in September 2014 placed the party 20 points ahead of the Tories. But much could change before polling day, and rather than going for a familiar face with plenty of campaign experience, Ukip has picked a 22-year-old as its candidate. Boston & Skegness will be either Ukip’s big breakthrough or a massive missed opportunity.

Heywood & Middleton

Can Ukip do what it almost managed to do in the by-election of October 2014 and win this constituency from Labour? The party has been tipping money and resources into the seat, believing it will be a case of second time lucky. A swing of just 1.1% is all Ukip needs to overturn Liz McInnes’ majority of 617. But Labour will also have learned from the outcome of the by-election, and will be fighting equally hard to hold on.

Rochester & Strood

I’ve no doubt that Douglas Carswell will hold Clacton for Ukip. Will his fellow Tory defector Mark Reckless do the same in Rochester & Strood? I’m not so sure. Reckless’ majority is only 2,920. The Tories need a swing of 3.7% to take back the seat, and whether they manage it will be a good marker of their success in wooing back erstwhile Ukip supporters.

Greens

Bristol West

Can the Greens double their representation in the Commons from one to two? Bristol West is the party’s top target, but candidate Darren Hall would need a swing of 22.1% to win, and this Lib Dem-held seat is also being targeted by Labour and the Tories. The Greens polled 3.8% here in 2010, and believe they will do better this time thanks to both the Lib Dem and Labour vote collapsing in their favour. The party also has six Bristol councillors – though admittedly this is on a council of 70.

Hove

The Greens won’t win here, but it’s their impact on the Labour vote that will be worth watching. Hove is a top Labour target, and would need a swing of only 1.9% to slip from the Conservatives’ grasp. However this is a seat in which the Greens polled 5.2% of the vote in 2010. If they increase their share of the vote this time, sucking a sizeable chunk of support from Labour in the process, Hove could remain in Tory hands. Labour would be furious at this result – but it may turn out to be typical of a number of marginals across the country.

SNP

Ochil & South Perthshire

The SNP’s “easiest” gain from Labour, but I’m using inverted commas because a swing of 5.2% is by no means easy. I expect the party to manage it, but the real test will be whether they manage it by some margin, or whether the result is close. Labour’s majority here in 2010 was 5,187. An SNP majority of a similar size would spell joy for the nationalists and panic for Labour; but an SNP majority of 1,000 or below might suggest Labour will hold on to most of its seats across Scotland.

Gordon

The Lib Dems’ Malcolm Bruce is stepping down from this seat after 32 years. Christine Jardine is hoping to succeed him, and only one person stands in her way. Unfortunately for Jardine, that person is Alex Salmond, and he will attract not just a mighty battery of SNP supporters but a similarly-sized pack of reporters. It will be a very tough, and very high-profile, contest. Salmond needs a 6.9% swing to take the seat. Watch to see how closely or how comfortably he achieves this.

Inverness, Nairn, Badenoch & Strathspey

A juicy target for the SNP, for if they win it from the Lib Dems, they’ll not only have managed a swing of 11% but unseated the secretary to the treasury Danny Alexander. A total of three Lib Dem seats would fall to the SNP on a swing of this size – but another three would change hands if the nationalists manage to push the swing one point higher to 12%. As such Alexander’s fate will be a good guide to whether the Lib Dems are heading for only a few losses in Scotland or near-obliteration.

Edinburgh East

This is a potential five-way battle between Labour, the SNP, the Liberal Democrats, the Tories and the Greens, and as such will be one most intriguing contests in all of Scotland. The Greens polled 5.1% in 2010. The SNP polled 20.4%, and need a 11.5% swing to take the seat. Just how will the anti-Tory/left-wing vote split? Might there be movement not just between Labour and the SNP, but also from the Lib Dems to Labour and Labour to the Greens? If the Labour/Lib Dem vote collapses entirely, will more of it go to the SNP than the Greens? And so on.

Glasgow East

The SNP needs a whopping 18.4% swing to win this from Labour. I’ve included it as an example of the sort of seat where a change of party would signal an almighty electoral earthquake was under way in Scotland. Other Glasgow constituencies may switch from Labour to the SNP – I’ve included one, Glasgow South, on my list of Labour seats to watch – but were Glasgow East to fall it would be a disaster for Ed Miliband (not to mention Jim Murphy) and a triumph for Nicola Sturgeon. Remember this constituency was won by the SNP in a by-election in 2008, but Labour won it back in 2010.