Many of these client trades expired earlier in April, when the Halifax house price index for March was published. So IG felt able to start accepting new bets again a fortnight ago.
Of last year's crop of pessimistic punters, the ones that did best were those that made down-bets on house prices early in 2004, before Bank of England Governor Mervyn King's stern warning on 15 June about possible property price falls.
IG said several of these clients made profits of more than £100,000 each. Those that made down-bets on prices later in the summer ended up more or less allsquare when the bets expired with the publication of the Halifax's March house price indices.
The bookie's latest prices project a future for property values that is fairly close to the Halifax's official forecast of a 2% fall in UK house prices this year and a 4% drop in London. However, both are more pessimistic than the Nationwide, which has been forecasting a rise of up to 5% in UK house prices in 2005.
Yesterday's prices from IG indicate the likelihood of falls in property values in every region. In the South-East, for instance, they suggest a fall on the Halifax measure of 4.7% in the year to next March; in Wales the implied fall is 3%.
This similar pattern across the country marks a change from last year when spread-betting prices were predicting a much worse price recession in London and the South-East than in the North, Wales and Scotland.
People who are active in speculating on house prices range from wealthy investors looking to hedge the value of their own homes to property professionals trying to anticipate the market's direction.
Anyone who does bet has to contend with a rather wide spread between the bid and offer prices, so there is no point in anyone speculating unless they think they can make profits of more than one or two percentage points.
A speculator on the London price could make a down-bet from the bottom of IG's spread for March 2006, at £229,000, or an up-bet from the top of the spread at £236,700.
Halifax earlier this month published a 'standard average price' for a property in London in March of £241,918, up just 0.1% compared with December and 1.1% higher than a year earlier.
However, unless prices rise between March and June, by the summer the annual house price inflation rate in London on the Halifax index is likely to be modestly negative.