The Asda Income Tracker has exposed a glaring north-south divide in disposable income while nationwide family spending power is at its lowest since the collapse of Lehman Brothers in 2008.

The grocer said UK families were £10 a week worse off in March than a year earlier with a £144 average of discretionary spend, 6.5% lower than last year.

Discretionary cash is also declining year-on-year across every UK region, with annual drops remaining severe in the first quarter of the year.

The north west of England and Northern Ireland saw strongest pressure on family budgets over the past year with just £136 and £83 of discretionary spend in the first quarter respectively. This compares to £148 and £90 in the first quarter of 2011.

Discretionary spend in London was £184 per week in the first quarter, four times higher than cash available to families in North West and Northern Ireland.

The official measure of the rising cost of living was up in February, as the consumer price index (CPI) rose over the year by 3.5%, well above average earnings growth which remained weak at just 1.6%.

Asda Mumdex research has revealed that two thirds of those surveyed budget more now that they did a year ago and 39% also say they have made changes to their lifestyle because of the financial crisis.

Asda president and chief executive Andy Clarke said:“It’s worrying to see the cost of essentials creeping back up, increasing the demands on family budgets and putting pressure income growth.

“Unemployment drove the continued drop in disposable income in March and throughout the quarter, with a growing divide between the nations and regions.

He added: “We’re firm in our commitment to help tackle this in 2012, by creating new jobs, working with new communities and bringing Asda value where it matters most to families across the UK.”

Last week Asda cut up to 2p a litre from the price of both unleaded and diesel, the first fall in prices in 2012.