Sound advice given as usual by Buildersmate and a good link given by boxtops providing more info as to what form the training agreement should take.
Just to add my twopence worth, we have training agreements that have been approved by our employment advisor RBS Mentor. As the link provided by boxtops states, the agreement must be separate to the employee contract, any monies taken must be on a sliding downwards scale according to the length of employment after the training has been completed, any training given must be completely separate to the day to day job that an employee does i.e it cannot be on job training. Also the employer must be able to prove the costs quoted are genuine provable costs, they cannot pull figures out of a hat to quote to an employee. I can confirm with our company that if an employee leaves falling within the above criteria, we can and have taken money from final salaries!
Hope the extra info helps.
Sue