Robin Bennett, managing director of London Tutors, said that although his agency has banned its teachers from helping with coursework, others may be duped or turn a blind eye to helping pupils cheat on coursework assignments.
"We threaten our tutors with fire and brimstone if they help with coursework. I also make it clear to callers we are not in the business of doing it, " said Mr Bennett.
It is not uncommon for A-level pupils to use their mobile phones to seek help from the agency, which arranges private tuition. They leave their mobile numbers so their parents do not realise what they are up to. Pupils are also prepared to pay Pounds 16 per hour from their savings for the lessons.
Mr Bennett said pupils often use subterfuge to get help: "They can be cunning. They will say they need help with history and then for the first half-hour will receive tuition before saying they want help with a particular piece of work, and ask for comments and suggestions. The teacher then feels he has been led up the garden path. One girl who turned up with maths coursework stormed out when the teacher said he would not help.
"I am beginning to believe that coursework should be scrapped because it is open to abuse. We do not tend to get requests for help for GCSE coursework because parents can usually do that. It is when you get to A-level or beyond that professional help is required."
Recently, almost a quarter of the calls to London Tutors have been from people looking for help with their assignments. Mr Bennett has noticed a sudden flurry of enquiries from science undergraduates. He wants to set up a register of tuition agencies, with a code of practice.
He said: "I want students to realise that we are on to them. Many of them don't even seem to think they are cheating. It is unfair to the other students and to the tutor involved. Some agencies are no more than retired teachers working from their front room. This sort of work is bread and butter to them, and must at times be difficult to turn down."
Mr Bennett wants to be able to blacklist pupils who try to cheat at coursework, by circulating their names to other agencies.