Lets first assume that the Greens will hold all their current seats in Regency (2), Queens Park (3), St Peters and North Laine (3) and Hanover and Elm Grove (3) wards.
So that is 11 seats, plus the one they have in Preston Park and the one in Goldsmid making the 13 they currently have.
I think it is safe to also assume they will pick up the other 2 seats in Goldsmid and possibly the 2 other seats in Preston Park, which gives the Greens a total of 17 seats, so far..
In the recent Goldsmid by-election the parties achieved the following swings:-
Lib Dem -7.3%
I thought I would translate this result across the city to see what would happen. I assumed in my naive way that this would help the Greens since they were the only party to gain votes, I had a nasty shock. I forgot we are talking about the first-past-the-post system here, that punishes heavily parties with similar ideologies that consequently split their supporters votes.
For simplicity I have left out very safe wards. The wards that are most marginal and the ones with actual changes are listed below.
So first off, lets look at how this affects the Brunswick and Adelaide ward result:-
surprisingly LIB DEM HOLD 2 seats, though only by 108 votes from Greens.
Lib Dem 873 (942)
Lib Dem 675 (729)
Green 567 (482)
Green 506 (431)
The following is a truly shocking result which happens as a result of the left vote being split three ways.
Moulsecomb & Bevendean - TORY GAIN 2 & HOLD 1 seat
Tory 979 (984)
Tory 978 (983)
Tory 959 (964)
Labour 948 (1010)
Labour 948 (1010)
Labour 790 (848)
Green 550 (468)
So, after looking at this I have revised down my Green seat prediction to no more than 19 seats in 2011 and possibly only 15 when before I optimistically had said they could get 21 seats.
I think the Greens will do better than Goldsmid swing in Brunswick/Adelaide ward, especially if Lucas becomes MP for Pavilion.
Also, maybe Preston Park might keep its 2 popular Labour members and the Labour vote is bound to bounce back a bit when the Tories are in Westminster - the other wards are far too safe for the Greens to take.
There is a risk the Tories might add a seat or two in North and South Portslade at Labour's expense bringing their total up to 26 which with the Tory independent, would be enough for them to again take control of the council. With the 2 seats gained in Moulsecomb & Bevendean the Tories would have 28 seats and total control with or without the independent.
Oh, the vagaries of our electoral system that gives power to one party that only need to achieve about 30% of the total vote to win absolute power. Sickening.