The average property price in the capital is now pound;175,000, according to the latest survey by the Halifax Bank. A standard mortgage would require an annual salary of more than pound;50,000 and a sizeable deposit.
Teachers who have crossed the performance threshold currently earn pound;26,919. Those in inner London receive an additional pound;3,000, known as the London allowance, to help with higher living costs in the capital. Outer London teachers receive an extra pound;1,974 and those in areas just outside London, including parts of Essex, get pound;765.
The National Union of Teachers will hold a one-day strike in the capital next Thursday over what it describes as an "inadequate" increase of 3.5 per cent in next year's allowance. An NUT spokesperson said the union received 1,000 new membership enquiries on Wednesday, the day after the union's London members approved the action. "This sends a clear message to Estelle Morris about the strength of feeling among teachers," she said.
Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers, believes London allowances would need to rise by pound;20,000 to allow individual teachers to buy homes in the capital. "I have done many things in my time as a union official but even I would blush to put in a claim for a rise from pound;3,000 (the current inner London allowance) to pound;23,000," he said.
Mr de Gruchy expressed sympathy with the NUT's action but said that providing living accommodation for teachers could do more to ease recruitment and retention problems.
"Halls of residence would be a good idea for two or three years for young people without families and straight out of university."
As people got older and took on family commitments they should be given subsidised mortages to help them get established on the property ladder, he said.
What the unions agree on is the failure of teachers' pay to keep pace with the rising living costs in the capital. A TES poll of teachers published last month found that just six out of 10 teachers in London feel comfortably or well-off compared with eight out of 10 teachers across England and Wales.
Many of the capital's schools rely on foreign supply teachers. Official figures show that in Hammersmith and Fulham almost 20 per cent of teachers are short-term supply staff. In Hackney, Islington, Kensington and Chelsea, Newham and Tower Hamlets it is about one in 10. The problem is not confined to inner London. At about pound;120,000, starter homes in Hounslow, near Heathrow airport, cost around the same as in inner-city Camden.
Gillian Smith, head of Feltham community college in Hounslow, said: "I've just lost three staff due to high housing costs. A couple of years ago we'd get 10 to 12 applications for every job, now we're lucky to get two or three."
Teachers at 200 Essex schools qualify for the "fringe" allowance. House prices, have gone up 10 per cent in the past 12 months, and have doubled over the past 10 years.
Tom Ramsbottom, who teaches in Basildon, bought his home for pound;55,000 in 1992. It is now worth pound;110,000, but he still could not "move up"the housing ladder. He said: "I've taught for 20 years in Basildon. I don't want to leave, but if I did move to another area I'd stand to make a big gain. If I was a new teacher I couldn't afford to live here at all."