When the ward-by-ward voting results from the London Assembly elections are released tomorrow, the music will begin in a game of musical seats for the MPs of Croydon and Sutton. ANDREW PELLING offers this guide to how things might be shaping up for Messrs Barwell, Brake and Burstow

Don’t put your anoraks away just yet. It’s still raining and nerds are about to pore over the detailed results from the London elections, broken down by ward.

Political parties will look to see which local government wards are worth targeting in the 2014 local elections.

Conservatives in Waddon and LibDems in Beddington North will hope to see no discernible impact on their vote as a consequence of their support for the Beddington Lane incinerator. After all, the Conservatives dismissed Sunday’s anti-incinerator march as being no longer than a bus queue. If bus queues of 100-strong are becoming the norm in London, then Mayor Boris needs to work a lot harder on the bus service.

Before this extra London election data is released, it is worthwhile looking at how the latest results might reflect on the re-election prospects for the area’s MPs.

The Liberal Democrats may yet object to the Boundary Commissioners’ recommended parliamentary boundary changes, but the conjunction of local elections in London with the General Election allows an easier analysis of how these new seats will play out. Employing local election results also allows a wash out of the distorting impact on baseline figures of my own participation as an independent in Croydon Central in the May 2010 General Election.

It must be assumed that strong incumbents like Sutton MPs Tom Brake and Paul Burstow will be able to hold back say one-third of the defectors from the LibDems that recent national opinion polls suggest in the areas they have represented.

How the new Purley and Carshalton constituency will look if the Boundary Commissioners’ recommendations are accepted

But for these MPs, exporting this “incumbency effect” into wards in what were formerly neighbouring seats will be more difficult. Efforts by Brake to achieve this in Croydon in this month’s London elections failed miserably.

Carshalton MP Tom Brake: will his “incumbency effect” carry over into areas of Croydon in a revised constituency?

Brake, MP for Carshalton and Wallington, will be forced to fight a revised constituency in 2015 if the Boundary Commissioners get their way. It seems unlikely that he will opt for the new Purley and Carshalton seat, where 63 per cent of the votes cast in the local elections in 2010 (after uprating for single and double candidatures by minority parties in three-seat wards) were in the solidly Conservative Croydon South constituency.

Looking at the 2010 local election results, this southerly seat is a clear Tory win over the Liberal Democrats with a 13.7 per cent Labour vote that is too small for the LibDems to squeeze to enable them to overtake the Tories.

A tradition of LibDem voting in Coulsdon East might aid their cause. In reality, this looks like a better prospect for LibDems in 2020, once they have targeted Conservative council seats in a couple of local elections.

The latest opinion polls would suggest that the existing unaltered parliamentary seats would deliver three Conservatives and two Labour MPs, with Croydon Central providing a 6 per cent Labour majority.

This seat, however, is made much easier for the Conservatives with the proposed boundary changes to become Croydon East, with the gain of the super-safe Tory Selsdon and Ballards ward in exchange for losing the more marginal Fairfield ward.

Croydon East will, like its Croydon Central predecessor, be a Labour versus Conservative contest and will be a Tory seat except in circumstances like those currently existing where the LibDems are pole axed and the Tories well behind. Today’s opinion polls – with Labour holding a record 14 per cent advantage on the Tories – would give Labour the narrowest of positive in this seat.

How the Boundary Commissioners see the new Sutton-Croydon seat of Croydon Central and St Helier

The Croydon Central and St Helier seat did throw up a vote of more than 20 per cent for the LibDems in local election wards in Croydon borough. This could give Brake hope in seat that is also made up of 49 per cent of local election votes cast in wards where he already enjoys incumbency.

In 2010 this seat would be a marginal Tory win, with a chunky 23.1 per cent Labour vote for LibDems to have squeezed to reverse that outcome.

Assuming that Brake is unable to transfer his “incumbency effect” across the Croydon borough boundary but nevertheless hold back one-third of LibDem voters from desertion in his old part of his constituency, this seat would in current political conditions could be a very marginal Labour win. If Brake was able to outperform those parameters, the seat would be won by the Conservatives currently, as Labour would gain fewer defecting LibDem voters to enable them to catch the Tories.

Let’s see whether the London Election results by ward, distorted by the non-inclusion of postal votes, also reveal these trends.

• Inside Croydon: Living life on the fringes of Croydon. Post your comments on this article below. If you have a news story about life in or around Croydon, email us at inside.croydon@btinternet.com

Related articles

• The Croydon woman who must try to keep Boris in check (insidecroydon.com)
• St Helier decision puts Sutton MP Burstow on the spot (insidecroydon.com)
• Sutton LibDem councillor switches to Labour over incinerator (insidecroydon.com)