The Liberal Democrats targeted the student vote today by warning that tuition fees could rise to £7,000 a year under the Tories or Labour.The party calculates that a student in London could be left more than £44,000 in debt from fees and maintenance loans after a three- year course ending in 2015.Lib Dem leader Nick Clegg pledged to oppose any attempt to remove the cap on tuition fees, warning of a "disaster" if student debt levels were allowed to rise further.Mr Clegg was in Oxford today for a question-and-answer session with students at Oxford Brookes University as he attempts to repeat that success in attracting the student vote in a race which opinion polls suggest could result in a hung Parliament.