Yesterday the review of the Parliamentary boundaries for the next general election kicked off – not that there is much to see yet. The English, Welsh, Scottish and Northern Ireland Boundary Commissions announced the beginning of the review, the electorate figures which they’ll be working off, and the number of seats that each country and region will be divided up into.

The review will be based on the same new rules as the review that was abandoned during the last Parliament. The amendment passed by Labour and the Lib Dems didn’t reverse the changes that the government had made to the rules on boundary reviews, they just delayed the next review for five years. This means the new review starts up now and will report in 2018, ready to be implemented for the 2020 election. This is not a case of the aborted review from the last Parliament being implemented, it’s a brand new review based on updated electorate numbers. However in terms of the broad strokes the proposals will be quite similar.

The boundary review will reduce the number of seats from 650 to 600, and go from boundaries based on 2001 electorates to boundaries based on 2015 electorates. Comparing the current boundaries to proposed new ones there will be some very substantial changes – it’s inevitable when fifty seats are being chopped. Comparing the numbers to what would have happened under the aborted review in the last Parliament the changes will be more modest.

Scotland will see its current 59 seats fall to 53 (compared to 52 in the aborted review), Wales will see its seat numbers fall from 40 to 29 (compared to 30 in the aborted review), Northern Ireland will get 17 seats (compared to 18 currently, 16 in the aborted review). Across the English regions the South East and East will lose 1 seat each, the East Midlands will lose 2 seats, North East 4, Yorkshire 4, London 5, West Midlands 6 and the North West 7. In most cases these figures are the same as the aborted review – the differences are that the West Midlands will lose an extra seat (probably in the Metropolitan area), the Eastern region will lose one less seat (it looks to me like Bedfordshire & Hertfordshire will no longer require a cross-county seat and the loss there will no longer happen, so Nadine Dorries will be reprieved) and the North East will lose an extra seat.

My calculations last year were that if the 2015 election had been fought on the boundaries from the aborted review it would have given the Conservatives a majority of 44. The Tories would have won nine fewer seats, Labour 28 fewer, the SNP six fewer and the Lib Dems just four. The impact of this new boundary review will likely be broadly similar, but perhaps a little worse for Labour: the extra seat reductions in the North East and West Midlands are likely to be Labour, the relative gains in the East Midlands and Scotland will be Conservative and SNP.

Those won’t the only differences though – we’ve had five years of population drift and the change in registration since then, so many of the proposals the boundary commissions made in 2012 would no longer add up anyway. Unavoidably, the detailed proposals will be different from what we saw in 2012. These won’t be extra seats created or abolished, just boundaries drawn in different ways. To give a couple of examples –

Coventry currently has three seats, and at the aborted review it still had just the right population to retain three seats for itself. Its electorate has now fallen to the point where it’s impossible to draw three seats that hit quota, so while there will still be three seats covering Coventry, one will have to take in some wards from outside Coventry, I’d guess from Warwickshire.

University seats saw a particular drop in the number of registered electors from the move to individual registration, so Cambridge constituency as it was previously proposed will no longer be large enough. There will still almost certainly be a Cambridge seat, but it will now probably cover the whole of the Cambridge council area and have to include a ward from outside Cambridge to make up the numbers.

Other areas where the electorate has dropped notably since the aborted boundary review include Blackpool, Leeds, Oxford, Kensington, Middlesbrough, Southampton, Carlisle and Newcastle. In places like these proposals will probably be substantially different to the aborted review – boundaries will need to move outwards, or the Commissions will choose to arrange the boundaries in completely different ways. At the other end of the scale, the electorate is notably higher in places like East Devon, Bedfordshire, Thanet, Greenwich and Bermondsey, so movement there is likely to be in the opposite direction.

In some cases those small adjustments will have a domino effect and require big changes through a whole county to make sure everything is in quota (though it is has been suggested that the English boundary commission will be more willing to split wards, making their task easier and – hopefully – avoiding some of the dafter proposals we saw last time). Even where there are small changes they may have party partisan effects here and there, making seats that little bit better or worse for parties, tipping the occasional marginal into the other column.

We won’t have any further details until the Commissions release their initial proposals, expected to be in September. At that point we will be able to start working out notional figures and coming up with detailed estimates of what the partisan impact of the boundary changes will be.