The increase in their workload has been caused by the Government's expansion drive, which has doubled the number of students in higher education and a tougher management style.
A new survey by the Association of University Teachers, which has 5,500 members in London and 31,000 nationally, has revealed that, on average, lecturers are working 57 hours a week. Many are working up to 70 hours.
The AUT asked 2,000 academics around the country to keep diaries of their working day. The results are still being analysed, but will be published next month.
The survey is expected to show that changes in higher education have taken their toll across the country. But researchers believe London's academics are likely to suffer additional stress.
Tom Wilson, research officer for the AUT, said: 'London academics cannot afford to live near the institutions where they work. They have to live in the suburbs. So as well as working a 12-hour day, they need to add two more hours for travelling. They are suffering from an increasing number of stress- related problems.'
Malcolm Keight, London representative of the AUT, said: 'One of the particular problems we have in London is that there are more mature students and overseas students, who need a great deal of support academically and emotionally.
'London has the highest drop-out rate for students. Many have taken out loans to get through their courses and are struggling with huge debts. Studying in London is expensive, because of the high cost of living and accommodation. Ironically, lecturers have less and less time to give that support to their students. It is a vicious circle.
'Our survey was of the old universities. It is highly probable that the hours worked at the newer universities is even more.'
Students, lecturers and even administrative staff at the old and new universities are suffering from depression and increasingly turning to counselling services. Some have had mental breakdowns or have simply quit.
Jill Jones, a lecturer at Westminster University (a former polytechnic) and London representative for the National Union of Teachers in Further and Higher Education (NATFHE), insists this is because lecturers feel devalued. 'Teaching now is like battery farming. Once we had the time to build rapport with students. Now we see them en masse.
At Westminster University requests for counselling increased from 231 to 314 last year.
Ms Jones sees this as proof that the system is not working. 'University and college managements insist they are committed to the British system of individual tutorials, while moving towards the American or European systems. It is a total contradiction in terms.'
The unions complain that the much-heralded expansion in student numbers was never matched by an increase in staffing levels.
Tomorrow London lecturer members of the AUT and NATFHE will lead a national day of action in protest over workloads, beginning with a rally at the Bloomsbury Theatre.
Ms Jones said: 'The old image of universities as sleepy seats of learning, where all the students come from the privileged classes, is now a fallacy.
'The pace is frenetic, the students do not have the quality of teaching that they once enjoyed because lecturers cannot spare the time - they are too busy carrying out all the administrative tasks.
'To have the expansion without extra funding and extra teachers is no progress at all. The whole system is cracking under the strain.'